Additive manufacturing of rubber-like materials

ABSTRACT

Methods of fabricating three-dimensional rubber-like objects which utilize one or more modeling material formulations which comprise an elastomeric curable material and silica particles are provided. Objects made of the modeling material formulations and featuring improved mechanical properties are also provided.

RELATED APPLICATIONS

This application is a National Phase of PCT Patent Application No.PCT/IL2017/050604 having International filing date of May 29, 2017,which claims the benefit of priority under 35 USC § 119(e) of U.S.Provisional Patent Application No. 62/342,970 filed May 29, 2016. Thecontents of the above applications are all incorporated by references asif fully set forth herein in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to additivemanufacturing (AM), and, more particularly, but not exclusively, toformulations and methods usable in additive manufacturing of an objectmade, in at least a portion thereof, of rubber-like material(s).

Synthetic rubbers are typically made of artificial elastomers. Anelastomer is a viscoelastic polymer, which generally exhibits lowYoung's modulus and high yield strain compared with other materials.Elastomers are typically amorphous polymers existing above their glasstransition temperature, so that considerable segmental motion ispossible. At ambient temperatures, rubbers are thus relatively soft,featuring elasticity of about 3 MPa, and deformable.

Elastomers are usually thermosetting polymers (or co-polymers), whichrequire curing (vulcanization) for cross-linking the polymer chains. Theelasticity is derived from the ability of the long chains to reconfigurethemselves to distribute an applied stress. The covalent cross-linkingensures that the elastomer will return to its original configurationwhen the stress is removed. Elastomers can typically reversibly extendfrom 5% to 700%.

Rubbers often further include fillers or reinforcing agents, usuallyaimed at increasing their hardness. Most common reinforcing agentsinclude finely divided carbon black and/or finely divided silica.

Both carbon black and silica, when added to the polymeric mixture duringrubber production, typically at a concentration of about 30 percent byvolume, raise the elastic modulus of the rubber by a factor of two tothree, and also confer remarkable toughness, especially resistance toabrasion, to otherwise weak materials. If greater amounts of carbonblack or silica particles are added, the modulus is further increased,but the tensile strength may be lowered.

Additive manufacturing is generally a process in which athree-dimensional (3D) object is manufactured utilizing a computer modelof the objects. Such a process is used in various fields, such as designrelated fields for purposes of visualization, demonstration andmechanical prototyping, as well as for rapid manufacturing (RM).

The basic operation of any AM system consists of slicing athree-dimensional computer model into thin cross sections, translatingthe result into two-dimensional position data and feeding the data tocontrol equipment which manufacture a three-dimensional structure in alayerwise manner.

Various AM technologies exist, amongst which are stereolithography,digital light processing (DLP), and three dimensional (3D) printing, 3Dinkjet printing in particular. Such techniques are generally performedby layer by layer deposition and solidification of one or more buildingmaterials, typically photopolymerizable (photocurable) materials.

In three-dimensional printing processes, for example, a buildingmaterial is dispensed from a dispensing head having a set of nozzles todeposit layers on a supporting structure. Depending on the buildingmaterial, the layers may then be cured or solidified using a suitabledevice.

Various three-dimensional printing techniques exist and are disclosedin, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334,7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,479,510, 7,500,846,7,962,237 and 9,031,680, all of the same Assignee, the contents of whichare hereby incorporated by reference.

A printing system utilized in additive manufacturing may include areceiving medium and one or more printing heads. The receiving mediumcan be, for example, a fabrication tray that may include a horizontalsurface to carry the material dispensed from the printing head. Theprinting head may be, for example, an ink jet head having a plurality ofdispensing nozzles arranged in an array of one or more rows along thelongitudinal axis of the printing head. The printing head may be locatedsuch that its longitudinal axis is substantially parallel to theindexing direction. The printing system may further include acontroller, such as a microprocessor to control the printing process,including the movement of the printing head according to a pre-definedscanning plan (e.g., a CAD configuration converted to a StereoLithography (STL) format and programmed into the controller). Theprinting head may include a plurality of jetting nozzles. The jettingnozzles dispense material onto the receiving medium to create the layersrepresenting cross sections of a 3D object.

In addition to the printing head, there may be a source of curingenergy, for curing the dispensed building material. The curing energy istypically radiation, for example, UV radiation.

Additionally, the printing system may include a leveling device forleveling and/or establishing the height of each layer after depositionand at least partial solidification, prior to the deposition of asubsequent layer.

The building materials may include modeling materials and supportmaterials, which form the object and the temporary support constructionssupporting the object as it is being built, respectively.

The modeling material (which may include one or more material(s)) isdeposited to produce the desired object/s and the support material(which may include one or more material(s)) is used, with or withoutmodeling material elements, to provide support structures for specificareas of the object during building and assure adequate verticalplacement of subsequent object layers, e.g., in cases where objectsinclude overhanging features or shapes such as curved geometries,negative angles, voids, and so on.

Both the modeling and support materials are preferably liquid at theworking temperature at which they are dispensed, and subsequentlyhardened, typically upon exposure to curing energy (e.g., UV curing), toform the required layer shape. After printing completion, supportstructures are removed to reveal the final shape of the fabricated 3Dobject.

Several additive manufacturing processes allow additive formation ofobjects using more than one modeling material. For example, U.S. patentapplication having Publication No. 2010/0191360, of the presentAssignee, discloses a system which comprises a solid freeformfabrication apparatus having a plurality of dispensing heads, a buildingmaterial supply apparatus configured to supply a plurality of buildingmaterials to the fabrication apparatus, and a control unit configuredfor controlling the fabrication and supply apparatus. The system hasseveral operation modes. In one mode, all dispensing heads operateduring a single building scan cycle of the fabrication apparatus. Inanother mode, one or more of the dispensing heads is not operativeduring a single building scan cycle or part thereof.

In a 3D inkjet printing process such as POLYJET™ (Stratasys Ltd.,Israel), the building material is selectively jetted from one or moreprinting heads and deposited onto a fabrication tray in consecutivelayers according to a pre-determined configuration as defined by asoftware file.

U.S. Pat. No. 9,227,365, by the present assignee, discloses methods andsystems for solid freeform fabrication of shelled objects, constructedfrom a plurality of layers and a layered core constituting core regionsand a layered shell constituting envelope regions.

Additive Manufacturing processes have been used to form rubber-likematerials. For example, rubber-like materials are used in POLYJET™systems as described herein. These materials are formulated to haverelatively low viscosity permitting dispensing, for example by inkjet,and to develop Tg which is lower than room temperature, e.g., −10° C. orlower. The latter is obtained by formulating a product with relativelylow degree of cross-linking and by using monomers and oligomers withintrinsic flexible molecular structure (e.g., acrylic elastomers).

An exemplary family of Rubber-like materials usable in POLYJET™ systems(marketed under the trade name “Tango” family) offers a variety ofelastomer characteristics, including Shore scale A hardness, elongationat break, Tear Resistance and tensile strength.

Rubber-like materials are useful for many modeling applicationsincluding: Exhibition and communication models; Rubber surrounds andover-molding; Soft-touch coatings and nonslip surfaces for tooling orprototypes; and Knobs, grips, pulls, handles, gaskets, seals, hoses,footwear.

SUMMARY OF THE INVENTION

In conventional production of elastomeric materials (elastomers,rubber-like materials), the starting material is typically athermoplastic polymer with low Tg, which is compounded and cured orvulcanized to achieve the desired final properties. In contrast, inadditive manufacturing processes such as 3D (inkjet) printing, a curedpolymer is produced in one stage from suitable monomers and/or lowmolecular weight cross-linkers and oligomers. Controlling the molecularweight, cross linking density and mechanical properties of the obtainedrubber-like materials in such processes is therefore challenging. Thus,for example, POLYJET™ rubber-like materials are often characterized bylow Tear Resistance (TR) value and/or slow return velocity afterdeformation, when compared, for example, to conventional elastomers.POLYJET™ rubber-like materials which exhibit high elongation are oftencharacterized by low modulus, low Tear Resistance and/or low Tg andtackiness.

The present inventors have now uncovered that utilizing various types ofnano-sized silica particles, including, for example, finely-dividedhydrophilic silica, hydrophobic silica and acrylic-coated silica, in themanufacture of rubber-like materials, yields rubber-like materials withimproved mechanical properties. The present inventors have shown thatusing such a methodology, rubber-like materials featuring,simultaneously, improved elongation, modulus and Tear Resistance, can beobtained.

According to an aspect of some embodiments of the present inventionthere is provided a method of additive manufacturing of athree-dimensional object made of an elastomeric material, the methodcomprising sequentially forming a plurality of layers in a configuredpattern corresponding to the shape of the object, thereby forming theobject, wherein the formation of each of at least a few of the layerscomprises dispensing at least one modeling material formulation, andexposing the dispensed modeling material to curing energy to therebyform a cured modeling material, the at least one modeling materialformulation comprising an elastomeric curable material and silicaparticles.

According to some of any of the embodiments described herein, the silicaparticles have an average particle size lower than 1 micron.

According to some of any of the embodiments described herein, at least aportion of the silica particles feature a hydrophilic surface.

According to some of any of the embodiments described herein, at least aportion of the silica particles feature a hydrophobic surface.

According to some of any of the embodiments described herein, at least aportion of the silica particles comprise functionalized silicaparticles.

According to some of any of the embodiments described herein, at least aportion of the silica particles are functionalized by curable functionalgroups (e.g., (meth)acrylate groups).

According to some of any of the embodiments described herein, an amountof the silica particles in the modeling material formulation ranges fromabout 1% to about 20%, or from about 1% to about 15%, or from about 1%to about 10%, by weight, of the total weight of a modeling materialformulation comprising the particles.

According to some of any of the embodiments described herein, an amountof the silica particles in the modeling material formulation ranges fromabout 1% to about 20%, or from about 1% to about 15%, or from about 1%to about 10%, by weight, of the total weight of the one or more modelingmaterial formulation(s) or of a formulation system as described herein.

According to some of any of the embodiments described herein, a weightratio of the elastomeric curable material and the silica particlesranges from about 30:1 to about 4:1.

According to some of any of the embodiments described herein, an amountof the elastomeric curable material is at least 40%, or at last 50%, byweight, of a total weight of a modeling material formulation comprisingthe material.

According to some of any of the embodiments described herein, an amountof the elastomeric curable material is at least 40%, or at last 50%, byweight, of a total weight of the one or more modeling materialformulation(s) or of a formulation system as described herein.

According to some of any of the embodiments described herein, theelastomeric curable material is selected from mono-functionalelastomeric curable monomer, mono-functional elastomeric curableoligomer, multi-functional elastomeric curable monomer, multi-functionalelastomeric curable oligomer, and any combination thereof.

According to some of any of the embodiments described herein, theelastomeric curable material and the silica particles are in the samemodeling material formulation.

According to some of any of the embodiments described herein, the atleast one modeling material formulation further comprises at least oneadditional curable material.

According to some of any of the embodiments described herein, theadditional curable material is selected from a mono-functional curablemonomer, a mono-functional curable oligomer, a multi-functional curablemonomer, a multi-functional curable oligomer and any combinationthereof.

According to some of any of the embodiments described herein, theelastomeric curable material, the silica particles and the additionalcurable material are in the same modeling material formulation.

According to some of any of the embodiments described herein, thedispensing is of one modeling material formulation.

According to some of any of the embodiments described herein, thedispensing is of two or more modeling material formulations.

According to some of any of the embodiments described herein, thedispensing is of at least two modeling material formulations and whereinone of the formulations comprises the elastomeric curable material andanother formulation comprises the additional curable material.

According to some of any of the embodiments described herein, the atleast one modeling material formulation further comprises at least oneadditional, non-curable material, for example, one or more of acolorant, an initiator, a dispersant, a surfactant, a stabilizer and aninhibitor.

According to some of any of the embodiments described herein, theelastomeric curable material is a UV-curable elastomeric material.

According to some of any of the embodiments described herein, the curingenergy comprises UV irradiation.

According to some of any of the embodiments described herein, theelastomeric curable material is an acrylic elastomer.

According to some of any of the embodiments described herein, the atleast modeling material formulation is characterized, when hardened, byTear Resistance of at least 4,000 N/m.

According to some of any of the embodiments described herein, the atleast modeling material formulation is characterized, when hardened, byTear Resistance higher by at least 500 N/m than a cured modelingmaterial devoid of the silica particles.

According to some of any of the embodiments described herein, the atleast modeling material formulation is characterized, when hardened, byTensile Strength of at least 2 MPa.

According to some of any of the embodiments described herein, the atleast one modeling material formulation is such that an objectconsisting of the cured modeling material and featuring two O-rings anda tube connecting the rings, such as, for example, depicted in FIGS.6A-C, is characterized by Tear Resistance under constant elongation ofat least one hour, or at least one day.

According to some of any of the embodiments described herein, thedispensing is of at least two modeling material formulations and is in avoxelated manner, wherein voxels of one of the modeling materialformulations are interlaced with voxels of at least one another modelingmaterial formulation.

According to some of any of the embodiments described herein, thedispensing is of at least two modeling material formulations, and issuch that forms a core region and one or more envelope regions at leastpartially surrounding the core region, to thereby fabricate an objectconstructed from a plurality of layers and a layered core constitutingcore regions and a layered shell constituting envelope regions.

According to some of any of the embodiments described herein, the one ormore envelope regions comprise(s) a plurality of envelope regions.

According to some of any of the embodiments described herein, dispensingthe layers further comprises dispensing a support material formulation.

According to some of any of the embodiments described herein, the methodfurther comprises, subsequent to the exposing, removing the supportmaterial.

According to an aspect of some embodiments of the present inventionthere is provided a three-dimensional object prepared by the method asdescribed herein in any of the respective embodiments, the objectfeaturing at least one portion which comprises an elastomeric material.

According to an aspect of some embodiments of the present inventionthere is provided a formulation system comprising a curable elastomericmaterial and silica particles, as described herein in any of therespective embodiments, the formulation system comprising one or moreformulations.

According to some of any of the embodiments described herein, an amountof the silica particles in the formulation system ranges from 1 to 20,or from 1 to 15, or from 1 to 10, weight percent, of the total weight ofthe formulation system.

According to some of any of the embodiments described herein, a weightratio of a total weight of the elastomeric curable material and a totalweight of the silica particles, in the formulation system, ranges from30:1 to 4:1.

According to some of any of the embodiments described herein, an amountof the elastomeric curable material in the formulation system is atleast 40%, or at least 50%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, theelastomeric curable material is selected from a mono-functionalelastomeric curable monomer, a mono-functional elastomeric curableoligomer, a multi-functional elastomeric curable monomer, amulti-functional elastomeric curable oligomer, and any combinationthereof.

According to some of any of the embodiments described herein, theelastomeric curable material and the silica particles are in the sameformulation.

According to some of any of the embodiments described herein, theformulation system further comprises at least one additional curablematerial.

According to some of any of the embodiments described herein, theadditional curable material is selected from a mono-functional curablemonomer, a mono-functional curable oligomer, a multi-functional curablemonomer, a multi-functional curable oligomer and any combinationthereof.

According to some of any of the embodiments described herein, theelastomeric curable material, the silica particles and the additionalcurable material are in the same formulation.

According to some of any of the embodiments described herein, theformulation system comprises one formulation.

According to some of any of the embodiments described herein, theformulation system comprises two or more formulations.

According to some of any of the embodiments described herein, theformulation system comprises at least two formulations, wherein one ofthe formulations comprises the elastomeric curable material and anotherformulation comprises the additional curable material.

According to some of any of the embodiments described herein, theformulation system further comprises at least one additional,non-curable material.

According to some of any of the embodiments described herein, thenon-curable material is selected from a colorant, an initiator, adispersant, a surfactant, a stabilizer, an inhibitor, and anycombination thereof.

According to some of any of the embodiments described herein, theformulation system comprises at least one elastomeric mono-functionalcurable material, at least one elastomeric multi-functional curablematerial and at least additional mono-functional curable material.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 10% to30%, by weight of the total weight of the formulation system.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric mono-functional curable material rangesfrom 50% to 70%, by weight of the total weight of the formulationsystem.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 20%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 10% to30%, by weight; a total concentration of the elastomeric mono-functionalcurable material ranges from 50% to 70%, by weight; and a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 20%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 20% to30%, by weight, of the total weight of the formulation system.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric mono-functional curable material rangesfrom 30% to 50%, by weight, of the total weight of the formulationsystem.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 30%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 20% to30%, by weight; a total concentration of the elastomeric mono-functionalcurable material ranges from 30% to 50%, by weight; and a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 30%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, theelastomeric curable material is a UV-curable elastomeric material.

According to some of any of the embodiments described herein, theelastomeric curable material is an acrylic elastomer.

According to some of any of the embodiments described herein, theformulation system as described herein in any of the respectiveembodiments is for use in additive manufacturing of a three-dimensionalobject, as a modeling material formulation system.

According to an aspect of some embodiments of the present inventionthere is provided a kit comprising the formulation system as describedherein in any of the respective embodiments.

According to some of any of the embodiments described herein, theformulation system comprises at least two formulations, and wherein eachof the formulations is individually packaged within the kit.

According to some of any of the embodiments described herein, theformulation system provides, when hardened, a material characterized byTear Resistance of at least 4,000 N/m.

According to some of any of the embodiments described herein, theformulation system provides, when hardened, a material characterized byTear Resistance higher by at least 500 N/m than a hardened materialdevoid of the silica particles.

According to some of any of the embodiments described herein, theformulation system provides, when hardened, a material characterized byTensile Strength of at least 2 MPa.

According to some of any of the embodiments described herein, an objectconsisting of the formulation, when hardened, and featuring two O-ringsand a tube connecting the rings, is characterized by Tear Resistanceunder constant elongation of at least one hour, or at least one day.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIGS. 1A-D are schematic illustrations of a representative andnon-limiting example of a system suitable for additive manufacturingaccording to some embodiments of the present invention;

FIGS. 2A-C are schematic illustrations of dispensing heads according tosome embodiments of the present invention;

FIG. 3 is a flowchart diagram of a method suitable for fabricating anobject by additive manufacturing according to aspects of someembodiments of the present invention;

FIG. 4 is a schematic illustration of a region which includes interlacedmodeling materials;

FIGS. 5A-D are schematic illustrations of a representative andnon-limiting example of a structure according to some embodiments of thepresent invention;

FIGS. 6A-C present schematic illustrations of an object (FIG. 6A) and astretching device (FIG. 6B) used in measuring static Tear Resistance inthe O-Ring test, according to some embodiments of the present invention,and a photograph presenting an exemplary such assay before (rightobject) and after (left object) subjecting the sample to elongationstress (FIG. 6C);

FIG. 7 presents comparative plots showing the effect of variousconcentrations of a hydrophobic, acrylic coated fumed silica, silicaR7200, on the stress-strain curves of a 3D inkjet-printed object made ofa rubbery material obtained from the respective formulation;

FIG. 8 presents comparative plots showing the effect of variousconcentrations of a hydrophobic, acrylic coated fumed silica, silicaR7200, and of 10% (hydrophilic) colloidal silica (silica nanopowder), onthe stress-strain curves of 3D inkjet-printed object made of a rubberymaterial obtained from the respective formulation;

FIG. 9 presents a water pipe connector printed using an exemplaryformulation according to some embodiments of the present invention (lefttube) and a water pipe connector printed using a formulation which doesnot contain silica (right tube), upon being fitted on a water tube for10 hours.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to additivemanufacturing (AM), and, more particularly, but not exclusively, toformulations and methods usable in additive manufacturing of an objectmade, in at least a portion thereof, of rubber-like material(s).

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

As discussed hereinabove, in contrast to conventional production ofelastomeric materials, in additive manufacturing processes such as 3D(inkjet) printing, a cured polymer is produced in one stage fromsuitable curable components, rendering the control of chemical andmechanical properties of the obtained rubber-like materials in suchprocesses challenging. Thus, current technologies for additivemanufacturing often result in rubber-like materials characterized by lowTear Resistance (TR) value and/or slow return velocity afterdeformation, when compared, for example, to conventional elastomers,whereby rubber-like materials which exhibit high elongation are oftencharacterized by low modulus, low Tear Resistance and/or low Tg andtackiness.

The present inventors have now uncovered that utilizing various types ofsub-micron (e.g., nano-sized) silica particles, including, for example,finely-divided hydrophilic silica, hydrophobic silica and functionalized(e.g., acrylic-coated) silica, in additive manufacturing (e.g., 3Dinkjet printing) of rubber-like materials, yields rubber-like materialswith improved mechanical properties. The present inventors have shownthat using such a methodology, rubber-like materials featuring,simultaneously, improved elongation, elastic modulus and TearResistance, can be obtained.

As demonstrated in the Examples section that follows, adding sub-micronsilica particles to formulations currently practiced in 3D inkjetprinting of rubber-like materials results in printed objects featuringTear Resistance higher by at least 500 N/m, and elastic modulus higherby at least 2-folds, compared to objects made of currently practicedformulations, and by a substantial improvement in resistance to tearunder constant elongation, from a few minutes/hours to several days,without compromising, and even improving, other properties, such aselongation and tensile strength. Such improved mechanical propertieswere demonstrated upon utilizing silica particles in an amount of up to10% by weight, of the total weight of the formulation.

Referring now to the drawings, FIGS. 1A-5D present schematicillustrations of exemplary systems, methods and structures according tosome embodiments of the present invention. FIGS. 6A-C present schematicillustrations and a photograph showing measurements of Tear Resistanceunder constant elongation; FIGS. 7 and 8 show that addition of increasedamounts of acrylic-coated silica particles results in increased elasticmodulus of the obtained rubber-like material. FIG. 9 presentsphotographs showing the improved Tear Resistance of rubber-likematerials made of formulations containing silica particles, according tosome embodiments of the present invention, upon usage in water tubes.Tables 1-4 in the Examples section that follows further present theimproved mechanical properties of rubber-like materials obtained in 3Dinkjet printing of formulations containing silica particles.

Herein throughout, the phrases “rubber”, “rubbery materials”,“elastomeric materials” and “elastomers” are used interchangeably todescribe materials featuring characteristics of elastomers. The phrase“rubbery-like material” or “rubber-like material” is used to describematerials featuring characteristics of rubbers, prepared by additivemanufacturing (e.g., 3D inkjet printing) rather than conventionalprocesses that involve vulcanization of thermoplastic polymers.

The term “rubbery-like material” is also referred to hereininterchangeably as “elastomeric material”.

Elastomers, or rubbers, are flexible materials that are characterized bylow Tg (e.g., lower than room temperature, preferably lower than 10° C.,lower than 0° C. and even lower than −10° C.).

The following describes some of the properties characterizing rubberymaterials, as used herein and in the art.

Shore A Hardness, which is also referred to as Shore hardness or simplyas hardness, describes a material's resistance to permanent indentation,defined by type A durometer scale. Shore hardness is typicallydetermined according to ASTM D2240.

Elastic Modulus, which is also referred to as Modulus of Elasticity oras Young's Modulus, or as Tensile modulus, or “E”, describes amaterial's resistance to elastic deformation when a force is applied,or, in other words, as the tendency of an object to deform along an axiswhen opposing forces are applied along that axis. Elastic modulus istypically measured by a tensile test (e.g., according to ASTM D 624) andis determined by the linear slope of a Stress-Strain curve in theelastic deformation region, wherein Stress is the force causing thedeformation divided by the area to which the force is applied and Strainis the ratio of the change in some length parameter caused by thedeformation to the original value of the length parameter. The stress isproportional to the tensile force on the material and the strain isproportional to its length.

Tensile Strength describes a material's resistance to tension, or, inother words, its capacity to withstand loads tending to elongate, and isdefined as the maximum stress in MPa, applied during stretching of anelastomeric composite before its rupture. Tensile strength is typicallymeasured by a tensile test (e.g., according to ASTM D 624) and isdetermined as the highest point of a Stress-Strain curve, as describedherein and in the art.

Elongation is the extension of a uniform section of a material,expressed as percent of the original length as follows:

${{Elongation}\mspace{14mu}\%} = {\frac{{{Final}\mspace{14mu}{length}} - {{Original}\mspace{14mu}{length}}}{{Original}\mspace{14mu}{length}} \times 100.}$Elongation is typically determined according to ASTM D412.

Z Tensile elongation is the elongation measured as described herein uponprinting in Z direction.

Tear Resistance (TR), which is also referred to herein and in the art as“Tear Strength” describes the maximum force required to tear a material,expressed in N per mm, whereby the force acts substantially parallel tothe major axis of the sample. Tear Resistance can be measured by theASTM D 412 method. ASTM D 624 can be used to measure the resistance tothe formation of a tear (tear initiation) and the resistance to theexpansion of a tear (tear propagation). Typically, a sample is heldbetween two holders and a uniform pulling force is applied untildeformation occurs. Tear Resistance is then calculated by dividing theforce applied by the thickness of the material. Materials with low TearResistance tend to have poor resistance to abrasion.

Tear Resistance under constant elongation describes the time requiredfor a specimen to tear when subjected to constant elongation (lower thanelongation at break). This value is determined, for example, in an“O-ring” test as described in the Examples section that follows and inFIGS. 6A-C.

Embodiments of the present invention relate to formulations usable inadditive manufacturing of three-dimensional (3D) objects or parts(portions) thereof made of rubbery-like materials, to additivemanufacturing processes utilizing same, and to objects fabricated bythese processes.

Herein throughout, the term “object” describes a final product of theadditive manufacturing. This term refers to the product obtained by amethod as described herein, after removal of the support material, ifsuch has been used as part of the building material. The “object”therefore essentially consists (at least 95 weight percent) of ahardened (e.g., cured) modeling material.

The term “object” as used herein throughout refers to a whole object ora part thereof.

An object according to the present embodiments is such that at least apart or a portion thereof is made of a rubbery-like material, and isalso referred to herein as “an object made of a rubbery-like material”.The object may be such that several parts or portions thereof are madeof a rubbery-like material, or such that is entirely made of arubbery-like material. The rubbery-like material can be the same ordifferent in the different parts or portions, and, for each part,portion or the entire object made of a rubbery-like material, therubbery-like material can be the same or different within the portion,part or object. When different rubbery-like materials are used, they candiffer in their chemical composition and/or mechanical properties, as isfurther explained hereinafter.

Herein throughout, the phrases “building material formulation”, “uncuredbuilding material”, “uncured building material formulation”, “buildingmaterial” and other variations therefore, collectively describe thematerials that are dispensed to sequentially form the layers, asdescribed herein. This phrase encompasses uncured materials dispensed soas to form the object, namely, one or more uncured modeling materialformulation(s), and uncured materials dispensed so as to form thesupport, namely uncured support material formulations.

Herein throughout, the phrase “cured modeling material” or “hardenedmodeling material” describes the part of the building material thatforms the object, as defined herein, upon exposing the dispensedbuilding material to curing, and, optionally, if a support material hasbeen dispensed, also upon removal of the cured support material, asdescribed herein. The cured modeling material can be a single curedmaterial or a mixture of two or more cured materials, depending on themodeling material formulations used in the method, as described herein.

The phrase “cured modeling material” or “cured modeling materialformulation” can be regarded as a cured building material wherein thebuilding material consists only of a modeling material formulation (andnot of a support material formulation). That is, this phrase refers tothe portion of the building material, which is used to provide the finalobject.

Herein throughout, the phrase “modeling material formulation”, which isalso referred to herein interchangeably as “modeling formulation”,“model formulation” “model material formulation” or simply as“formulation”, describes a part or all of the building material which isdispensed so as to form the object, as described herein. The modelingmaterial formulation is an uncured modeling formulation (unlessspecifically indicated otherwise), which, upon exposure to curingenergy, forms the object or a part thereof.

In some embodiments of the present invention, a modeling materialformulation is formulated for use in three-dimensional inkjet printingand is able to form a three-dimensional object on its own, i.e., withouthaving to be mixed or combined with any other substance.

An uncured building material can comprise one or more modelingformulations, and can be dispensed such that different parts of theobject are made, upon curing, of different cured modeling formulationsor different combinations thereof, and hence are made of different curedmodeling materials or different mixtures of cured modeling materials.

The formulations forming the building material (modeling materialformulations and support material formulations) comprise one or morecurable materials, which, when exposed to curing energy, form hardened(cured) material.

Herein throughout, a “curable material” is a compound (typically amonomeric or oligomeric compound, yet optionally a polymeric material)which, when exposed to curing energy, as described herein, solidifies orhardens to form a cured material. Curable materials are typicallypolymerizable materials, which undergo polymerization and/orcross-linking when exposed to suitable energy source.

A curable material, according to the present embodiments, alsoencompasses materials which harden or solidify (cure) without beingexposed to a curing energy, but rather to a curing condition (forexample, upon exposure to a chemical reagent), or simply upon exposureto the environment.

The terms “curable” and “solidifyable” as used herein areinterchangeable.

The polymerization can be, for example, free-radical polymerization,cationic polymerization or anionic polymerization, and each can beinduced when exposed to curing energy such as, for example, radiation,heat, etc., as described herein.

In some of any of the embodiments described herein, a curable materialis a photopolymerizable material, which polymerizes and/or undergoescross-linking upon exposure to radiation, as described herein, and insome embodiments the curable material is a UV-curable material, whichpolymerizes and/or undergoes cross-linking upon exposure to UVradiation, as described herein.

In some embodiments, a curable material as described herein is aphotopolymerizable material that polymerizes via photo-inducedfree-radical polymerization. Alternatively, the curable material is aphotopolymerizable material that polymerizes via photo-induced cationicpolymerization.

In some of any of the embodiments described herein, a curable materialcan be a monomer, an oligomer or a short-chain polymer, each beingpolymerizable and/or cross-linkable as described herein.

In some of any of the embodiments described herein, when a curablematerial is exposed to curing energy (e.g., radiation), it hardens(cured) by any one, or combination, of chain elongation andcross-linking.

In some of any of the embodiments described herein, a curable materialis a monomer or a mixture of monomers which can form a polymericmaterial upon a polymerization reaction, when exposed to curing energyat which the polymerization reaction occurs. Such curable materials arealso referred to herein as monomeric curable materials.

In some of any of the embodiments described herein, a curable materialis an oligomer or a mixture of oligomers which can form a polymericmaterial upon a polymerization reaction, when exposed to curing energyat which the polymerization reaction occurs. Such curable materials arealso referred to herein as oligomeric curable materials.

In some of any of the embodiments described herein, a curable material,whether monomeric or oligomeric, can be a mono-functional curablematerial or a multi-functional curable material.

Herein, a mono-functional curable material comprises one functionalgroup that can undergo polymerization when exposed to curing energy(e.g., radiation).

A multi-functional curable material comprises two or more, e.g., 2, 3, 4or more, functional groups that can undergo polymerization when exposedto curing energy. Multi-functional curable materials can be, forexample, di-functional, tri-functional or tetra-functional curablematerials, which comprise 2, 3 or 4 groups that can undergopolymerization, respectively. The two or more functional groups in amulti-functional curable material are typically linked to one another bya linking moiety, as defined herein. When the linking moiety is anoligomeric or polymeric moiety, the multi-functional group is anoligomeric or polymeric multi-functional curable material.Multi-functional curable materials can undergo polymerization whensubjected to curing energy and/or act as cross-linkers.

The method of the present embodiments manufactures three-dimensionalobjects in a layerwise manner by forming a plurality of layers in aconfigured pattern corresponding to the shape of the objects, asdescribed herein.

The final three-dimensional object is made of the modeling material or acombination of modeling materials or a combination of modelingmaterial/s and support material/s or modification thereof (e.g.,following curing). All these operations are well-known to those skilledin the art of solid freeform fabrication.

According to an aspect of some embodiments of the present inventionthere is provided a method of additive manufacturing of athree-dimensional object made of an elastomeric (rubbery-like) material,as described herein.

The method is generally effected by sequentially forming a plurality oflayers in a configured pattern corresponding to the shape of the object,such that formation of each of at least a few of said layers, or of eachof said layers, comprises dispensing a building material (uncured) whichcomprises one or more modeling material formulation(s), and exposing thedispensed modeling material to curing energy to thereby form a curedmodeling material, as described in further detail hereinafter.

According to embodiments of the present invention, the one or moremodeling material formulation(s) comprise an elastomeric curablematerial and silica particles. The elastomeric curable material and thesilica particles can be in the same modeling material formulation, or,when two or more modeling material formulations are used, in differentmodeling material formulations.

In some exemplary embodiments of the invention an object is manufacturedby dispensing a building material (uncured) that comprises two or moredifferent modeling material formulations, each modeling materialformulation from a different dispensing head of the inkjet printingapparatus. The modeling material formulations are optionally andpreferably deposited in layers during the same pass of the printingheads. The modeling material formulations and/or combination offormulations within the layer are selected according to the desiredproperties of the object, and as further described in detailhereinbelow.

The phrase “digital materials”, as used herein and in the art, describesa combination of two or more materials on a microscopic scale or voxellevel such that the printed zones of a specific material are at thelevel of few voxels, or at a level of a voxel block. Such digitalmaterials may exhibit new properties that are affected by the selectionof types of materials and/or the ratio and relative spatial distributionof two or more materials.

In exemplary digital materials, the modeling material of each voxel orvoxel block, obtained upon curing, is independent of the modelingmaterial of a neighboring voxel or voxel block, obtained upon curing,such that each voxel or voxel block may result in a different modelmaterial and the new properties of the whole part are a result of aspatial combination, on the voxel level, of several different modelmaterials.

Herein throughout, whenever the expression “at the voxel level” is usedin the context of a different material and/or properties, it is meant toinclude differences between voxel blocks, as well as differences betweenvoxels or groups of few voxels. In preferred embodiments, the propertiesof the whole part are a result of a spatial combination, on the voxelblock level, of several different model materials.

The Modeling Material Formulation and Formulation System:

Elastomeric Curable Material:

One or more of the modeling material formulations usable in the methodas described herein comprises an elastomeric curable material.

The phrase “elastomeric curable material” describes a curable material,as defined herein, which, upon exposure to curing energy, provides acured material featuring properties of an elastomer (a rubber, orrubber-like material).

Elastomeric curable materials typically comprise one or morepolymerizable (curable) groups, which undergo polymerization uponexposure to a suitable curing energy, linked to a moiety that conferselasticity to the polymerized and/or cross-linked material. Suchmoieties typically comprise alkyl, alkylene chains, hydrocarbon,alkylene glycol groups or chains (e.g., oligo or poly(alkylene glycol)as defined herein, urethane, oligourethane or polyurethane moieties, asdefined herein, and the like, including any combination of theforegoing, and are also referred to herein as “elastomeric moieties”.

An elastomeric mono-functional curable material according to someembodiments of the present invention can be a vinyl-containing compoundrepresented by Formula I:

wherein at least one of R₁ and R₂ is and/or comprises an elastomericmoiety, as described herein.

The (═CH₂) group in Formula I represents a polymerizable group, and is,according to some embodiments, a UV-curable group, such that theelastomeric curable material is a UV-curable material.

For example, R₁ is or comprises an elastomeric moiety as defined hereinand R₂ is, for example, hydrogen, C(1-4) alkyl, C(1-4) alkoxy, or anyother substituent, as long as it does not interfere with the elastomericproperties of the cured material.

In some embodiments, R₁ is a carboxylate, and the compound is amono-functional acrylate monomer. In some of these embodiments, R₂ ismethyl, and the compound is mono-functional methacrylate monomer.Curable materials in which R₁ is carboxylate and R₂ is hydrogen ormethyl are collectively referred to herein as “(meth)acrylates”.

In some of any of these embodiments, the carboxylate group, —C(═O)—ORa,comprises Ra which is an elastomeric moiety as described herein.

In some embodiments, R₁ is amide, and the compound is a mono-functionalacrylamide monomer. In some of these embodiments, R₂ is methyl, and thecompound is mono-functional methacrylamide monomer. Curable materials inwhich R₁ is amide and R₂ is hydrogen or methyl are collectively referredto herein as “(meth)acrylamide”.

(Meth)acrylates and (meth)acrylamides are collectively referred toherein as (meth)acrylic materials.

In some embodiments, R₁ is a cyclic amide, and in some embodiments, itis a cyclic amide such as lactam, and the compound is a vinyl lactam. Insome embodiments, R₁ is a cyclic carboxylate such as lactone, and thecompound is a vinyl lactone.

When one or both of R₁ and R₂ comprise a polymeric or oligomeric moiety,the mono-functional curable compound of Formula I is an exemplarypolymeric or oligomeric mono-functional curable material. Otherwise, itis an exemplary monomeric mono-functional curable material.

In multi-functional elastomeric materials, the two or more polymerizablegroups are linked to one another via an elastomeric moiety, as describedherein.

In some embodiments, a multifunctional elastomeric material can berepresented by Formula I as described herein, in which R₁ comprises anelastomeric material that terminates by a polymerizable group, asdescribed herein.

For example, a di-functional elastomeric curable material can berepresented by Formula I*:

wherein E is an elastomeric linking moiety as described herein, and R′₂is as defined herein for R₂.

In another example, a tri-functional elastomeric curable material can berepresented by Formula II:

wherein E is an elastomeric linking moiety as described herein, and R′₂and R″₂ are each independently as defined herein for R₂.

In some embodiments, a multi-functional (e.g., di-functional,tri-functional or higher) elastomeric curable material can becollectively represented by Formula III:

Wherein:

R₂ and R′₂ are as defined herein;

B is a di-functional or tri-functional branching unit as defined herein(depending on the nature of X₁);

X₂ and X₃ are each independently absent, an elastomeric moiety asdescribed herein, or is selected from an alkyl, a hydrocarbon, analkylene chain, a cycloalkyl, an aryl, an alkylene glycol, a urethanemoiety, and any combination thereof; and

X₁ is absent or is selected from an alkyl, a hydrocarbon, an alkylenechain, a cycloalkyl, an aryl, an alkylene glycol, a urethane moiety, andan elastomeric moiety, each being optionally being substituted (e.g.,terminated) by a meth(acrylate) moiety (O—C(═O) CR″₂═CH₂), and anycombination thereof, or, alternatively, X₁ is:

wherein:

the curved line represents the attachment point;

B′ is a branching unit, being the same as, or different from, B;

X′₂ and X′₃ are each independently as defined herein for X₂ and X₃; and

R″₂ and R′″₂ are as defined herein for R₂ and R′₂.

provided that at least one of X₁, X₂ and X₃ is or comprises anelastomeric moiety as described herein.

The term “branching unit” as used herein describes a multi-radical,preferably aliphatic or alicyclic group. By “multi-radical” it is meantthat the linking moiety has two or more attachment points such that itlinks between two or more atoms and/or groups or moieties.

That is, the branching unit is a chemical moiety that, when attached toa single position, group or atom of a substance, creates two or morefunctional groups that are linked to this single position, group oratom, and thus “branches” a single functionality into two or morefunctionalities.

In some embodiments, the branching unit is derived from a chemicalmoiety that has two, three or more functional groups. In someembodiments, the branching unit is a branched alkyl or a branchedlinking moiety as described herein.

Multi-functional elastomeric curable materials featuring 4 or morepolymerizable groups are also contemplated, and can feature structuressimilar to those presented in Formula III, while including, for example,a branching unit B with higher branching, or including an X₁ moietyfeaturing two (meth)acrylate moieties as defined herein, or similar tothose presented in Formula II, while including, for example, another(meth)acrylate moiety that is attached to the elastomeric moiety.

In some embodiments, the elastomeric moiety, e.g., Ra in Formula I orthe moiety denoted as E in Formulae I*, II and III, is or comprises analkyl, which can be linear or branched, and which is preferably of 3 ormore or of 4 or more carbon atoms; an alkylene chain, preferably of 3 ormore or of 4 or more carbon atoms in length; an alkylene glycol asdefined herein, an oligo(alkylene glycol), or a poly(alkylene glycol),as defined herein, preferably of 4 or more atoms in length, a urethane,an oligourethane, or a polyurethane, as defined herein, preferably of 4or more carbon atoms in length, and any combination of the foregoing.

In some of any of the embodiments described herein, the elastomericcurable material is a (meth)acrylic curable material, as describedherein, and in some embodiments, it is an acrylate.

In some of any of the embodiments described herein, the elastomericcurable material is or comprises a mono-functional elastomeric curablematerial, and is some embodiments, the mono-functional elastomericcurable material is represented by Formula I, wherein R₁ is —C(═O)—ORaand Ra is an alkylene chain (e.g., of 4 or more, preferably 6 or more,preferably 8 or more, carbon atoms in length), or a poly(alkyleneglycol) chain, as defined herein.

In some embodiments, the elastomeric curable material is or comprises amulti-functional elastomeric curable material, and is some embodiments,the multi-functional elastomeric curable material is represented byFormula I*, wherein E is an alkylene chain (e.g., of 4 or more, or 6 ormore, carbon atoms in length), and/or a poly(alkylene glycol) chain, asdefined herein.

In some embodiments, the elastomeric curable material is or comprises amulti-functional elastomeric curable material, and is some embodiments,the multi-functional elastomeric curable material is represented byFormula II, wherein E is a branched alkyl (e.g., of 3 or more, or of 4or more, or of 5 or more, carbon atoms in length).

In some of any of the embodiments described herein, the elastomericcurable material is an elastomeric acrylate or methacrylate (alsoreferred to as acrylic or methacrylic elastomer), for example, ofFormula I, I*, II or III, and in some embodiments, the acrylate ormethacrylate is selected such that when hardened, the polymeric materialfeatures a Tg lower than 0° C. or lower than −10° C.

Exemplary elastomeric acrylate and methacrylate curable materialsinclude, but are not limited to, 2-propenoic acid,2-[[(butylamino)carbonyl]oxy]ethyl ester (an exemplary urethaneacrylate), and compounds marketed under the trade names SR335 (Laurylacrylate) and SR395 (isodecyl acrylate) (by Sartomer). Other examplesinclude compounds marketed under the trade names SR350D (a trifunctionaltrimethylolpropane trimethacrylate (TMPTMA), SR256(2-(2-ethoxyethoxy)ethyl acrylate, SR252 (polyethylene glycol (600)dimethacrylate), SR561 (an alkoxylated hexane diol diacrylate) (bySartomer).

It is to be notes that other acrylic materials, featuring, for example,one or more acrylamide groups instead of one or more acrylate ormethacrylate groups are also contemplated.

In some of any of the embodiments described herein, the one or moreelastomeric curable materials are included in the one or more modelingmaterial formulations, as described in further detail hereinunder.

In some of any of the embodiment described herein, the elastomericcurable material comprises one or more mono-functional elastomericcurable material(s) (e.g., a mono-functional elastomeric acrylate, asrepresented, for example, in Formula I) and one or more multi-functional(e.g., di-functional) elastomeric curable materials(s) (e.g., adi-functional elastomeric acrylate, as represented, for example, inFormula I*, II or III) and in any of the respective embodiments asdescribed herein.

In some of any of the embodiments described herein, a total amount ofthe elastomeric curable material(s) is at least 40%, or at last 50%, orat least 60%, and can be up to 70% or even 80%, of the total weight of amodeling material formulation(s) or a formulation system comprisingsame.

In some embodiments, the one or more modeling material formulation(s)comprise one modeling material formulation. In some embodiments, the oneor more modeling material formulation(s) comprise two or moreformulations, and the one or more elastomeric curable material(s) arecomprised within 1, 2 or all the formulations.

Hereinthroughout, the one or more modeling material formulation(s) arealso referred to herein as a formulation system, as described in furtherdetail hereinafter.

Silica Particles:

Each of the one or more modeling formulations comprises at least onecurable material, and at least one of the modeling formulationscomprises silica particles.

In some of any of the embodiments described herein, the silica particleshave an average particle size lower than 1 micron, namely, the silicaparticles are sub-micron particles. In some embodiments, the silicaparticles are nano-sized particles, or nanoparticles, having an averageparticle size in the range of from 0.1 nm to 900 nm, or from 0.1 nm to700 nm, or from 1 nm to 700 nm, or from 1 nm to 500 nm or from 1 nm to200 nm, including any intermediate value and subranges therebetween.

In some embodiments, at least a portion of such particles may aggregate,upon being introduced to the formulation. In some of these embodiments,the aggregate has an average size of no more than 3 microns, or no morethan 1.5 micron.

Any commercially available formulations of sub-micron silica particlesis usable in the context of the present embodiments, including fumedsilica, colloidal silica, precipitated silica, layered silica (e.g.,montmorillonite), and aerosol assisted self-assembly of silicaparticles.

The silica particles can be such that feature a hydrophobic orhydrophilic surface. The hydrophobic or hydrophilic nature of theparticles' surface is determined by the nature of the surface groups onthe particles.

When the silica is untreated, namely, is composed substantially of Siand O atoms, the particles typically feature silanol (Si—OH) surfacegroups and are therefore hydrophilic. Untreated (or uncoated) colloidalsilica, fumed silica, precipitated silica and layered silica all featurea hydrophilic surface, and are considered hydrophilic silica.

Layered silica may be treated so as to feature long-chain hydrocarbonsterminating by quaternary ammonium and/or ammonium as surface groups,and the nature of its surface is determined by the length of thehydrocarbon chains.

Hydrophobic silica is a form of silica in which hydrophobic groups arebonded to the particles' surface, and is also referred to as treatedsilica or functionalized silica (silica reacted with hydrophobicgroups).

Silica particles featuring hydrophobic surface groups such as, but notlimited to, alkyls, preferably medium to high alkyls of 2 or more carbonatoms in length, preferably of 4 or more, or 6 or more, carbon atoms inlength, cycloalkyls, aryl, and other hydrocarbons, as defined herein, orhydrophobic polymers (e.g., polydimethylsiloxane), are particles ofhydrophobic silica.

Silica particles as described herein can therefore by untreated(non-functionalized) and as such are hydrophilic particles.

Alternatively, silica particles as described herein can be treated, orfunctionalized, by being reacted so as to form bonds with the moietieson their surface.

When the moieties are hydrophilic moieties, the functionalized silicaparticles are hydrophilic.

Silica particles featuring hydrophilic surface groups such as, but notlimited to, hydroxy, amine, ammonium, carboxy, silanol, oxo, and thelike, are particles of hydrophilic silica.

When the moieties are hydrophobic moieties, as described herein, thefunctionalized silica particles are hydrophobic.

In some of any of the embodiments described herein, at least a portion,or all, of the silica particles feature a hydrophilic surface (namely,are hydrophilic silica particles, for example, of untreated silica suchas colloidal silica).

In some of any of the embodiments described herein, at least a portion,or all, of the silica particles feature a hydrophobic surface (namely,are hydrophobic silica particles).

In some embodiments, the hydrophobic silica particles are functionalizedsilica particles, namely, particles of silica treated with one or morehydrophobic moieties.

In some of any of the embodiments described herein, at least a portion,or all, of the silica particles are hydrophobic silica particles,functionalized by curable functional groups (particles featuring curablegroups on their surface).

The curable functional groups can be any polymerizable group asdescribed herein. In some embodiments, the curable functional groups arepolymerizable by the same polymerization reaction as the curablemonomers in the formulation, and/or when exposed to the same curingcondition as the curable monomers. In some embodiments, the curablegroups are (meth)acrylic (acrylic or methacrylic) groups, as definedherein.

Hydrophilic and hydrophobic, functionalized and untreated silicaparticles as described herein can be commercially available materials orcan be prepared using methods well known in the art.

By “at least a portion”, as used in the context of these embodiments, itis meant at least 10%, or at least 20%, or at least 30%, or at least40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%,or at least 90%, or at least 95%, or at least 98%, of the particles.

The silica particles may also be a mixture of two or more types ofsilica particles, for example, two or more types of any of the silicaparticles described herein.

In some of any of the embodiments described herein, an amount of thesilica particles in a modeling material formulation comprising sameranges from about 1% to about 20%, or from about 1% to about 15%, orfrom about 1% to about 10%, by weight, of the total weight of themodeling material formulation.

In some of any of the embodiments described herein, an amount of thesilica particles in a formulation system as described herein ranges fromabout 1% to about 20%, or from about 1% to about 15%, or from about 1%to about 10%, by weight, of the total weight of the formulation system.

In some embodiments, the formulation system comprises one formulation.In some embodiments, the formulation system comprises two or moreformulations, and the silica particles are comprised within 1, 2 or allthe formulations.

The amount of the silica particles can be manipulated as desired so asto control the mechanical properties of the cured modeling materialand/or the object or part therein comprising same. For example, higheramount of silica particles may result in higher elastic modulus of thecured modeling material and/or the object or part thereof comprisingsame.

In some of any of the embodiments described herein, an amount of thesilica particles is such that a weight ratio of the elastomeric curablematerial(s) and the silica particles in the one or more modelingmaterial formulation(s) ranges from about 50:1 to about 4:1 or fromabout 30:1 to about 4:1 or from about 20:1 to about 2:1, including anyintermediate values and subranges therebetween.

Additional Components:

According to some of any of the embodiments described herein, one ormore of the modeling material formulation(s) further comprises one ormore additional curable material(s).

The additional curable material can be a mono-functional curablematerial, a multi-functional curable material, or a mixture thereof, andeach material can be a monomer, an oligomer or a polymer, or acombination thereof.

Preferably, but not obligatory, the additional curable material ispolymerizable when exposed to the same curing energy at which thecurable elastomeric material is polymerizable, for example, uponexposure to irradiation (e.g., UV-vis irradiation).

In some embodiments, the additional curable material is such that whenhardened, the polymerized material features Tg higher than that of anelastomeric material, for example, a Tg higher than 0° C., or higherthan 5° C. or higher than 10° C.

Herein throughout, “Tg” refers to glass transition temperature definedas the location of the local maximum of the E″ curve, where E″ is theloss modulus of the material as a function of the temperature.

Broadly speaking, as the temperature is raised within a range oftemperatures containing the Tg temperature, the state of a material,particularly a polymeric material, gradually changes from a glassy stateinto a rubbery state.

Herein, “Tg range” is a temperature range at which the E″ value is atleast half its value (e.g., can be up to its value) at the Tgtemperature as defined above.

Without wishing to be bound to any particular theory, it is assumed thatthe state of a polymeric material gradually changes from the glassystate into the rubbery within the Tg range as defined above. Herein, theterm “Tg” refers to any temperature within the Tg range as definedherein.

In some embodiments, the additional curable material is anon-elastomeric curable material, featuring, for example, when hardened,Tg and/or Elastic Modulus that are different from those representingelastomeric materials.

In some embodiments, the additional curable material is amono-functional acrylate or methacrylate ((meth)acrylate). Non-limitingexamples include isobornyl acrylate (IBOA), isobornylmethacrylate,acryloyl morpholine (ACMO), phenoxyethyl acrylate, marketed by SartomerCompany (USA) under the trade name SR-339, urethane acrylate oligomersuch as marketed under the name CN 131B, and any other acrylates andmethacrylates usable in AM methodologies.

In some embodiments, the additional curable material is amulti-functional acrylate or methacrylate ((meth)acrylate). Non-limitingexamples of multi-functional (meth)acrylates include propoxylated (2)neopentyl glycol diacrylate, marketed by Sartomer Company (USA) underthe trade name SR-9003, Ditrimethylolpropane Tetra-acrylate (DiTMPTTA),Pentaerythitol Tetra-acrylate (TETTA), and DipentaerythitolPenta-acrylate (DiPEP), and an aliphatic urethane diacrylate, forexample, such as marketed as Ebecryl 230. Non-limiting examples ofmulti-functional (meth)acrylate oligomers include ethoxylated ormethoxylated polyethylene glycol diacrylate or dimethacrylate,ethoxylated bisphenol A diacrylate, polyethylene glycol-polyethyleneglycol urethane diacrylate, a partially acrylated polyol oligomer,polyester-based urethane diacrylates such as marketed as CNN91.

Any other curable materials, preferably curable materials featuring a Tgas defined herein, are contemplated as an additional curable material.

In some of any of the embodiments described herein, one or more of themodeling material formulation(s) further comprises an initiator, forinitiating polymerization of the curable materials.

When all curable materials (elastomeric and additional, if present) arephotopolymerizable, a photoinitiator is usable in these embodiments.

Non-limiting examples of suitable photoinitiators include benzophenones(aromatic ketones) such as benzophenone, methyl benzophenone, Michler'sketone and xanthones; acylphosphine oxide type photo-initiators such as2,4,6-trimethylbenzolydiphenyl phosphine oxide (TMPO),2,4,6-trimethylbenzoylethoxyphenyl phosphine oxide (TEPO), andbisacylphosphine oxides (BAPO's); benzoins and bezoin alkyl ethers suchas benzoin, benzoin methyl ether and benzoin isopropyl ether and thelike. Examples of photoinitiators are alpha-amino ketone,bisacylphosphine oxide (BAPO's), and those marketed under the tradenameIrgacure®.

A photo-initiator may be used alone or in combination with aco-initiator. Benzophenone is an example of a photoinitiator thatrequires a second molecule, such as an amine, to produce a free radical.After absorbing radiation, benzophenone reacts with a ternary amine byhydrogen abstraction, to generate an alpha-amino radical which initiatespolymerization of acrylates. Non-limiting example of a class ofco-initiators are alkanolamines such as triethylamine,methyldiethanolamine and triethanolamine.

A concentration of a photoinitiator in a formulation containing same mayrange from about 0.1 to about 5 weight percent, or from about 1 to about5 weight percent, including any intermediate value and subrangestherebetween.

According to some of any of the embodiments described herein, one ormore of the modeling material formulation(s) further comprises one ormore additional, non-curable material, for example, one or more of acolorant, a dispersant, a surfactant, a stabilizer and an inhibitor.

An inhibitor is included in the formulation(s) for preventing or slowingdown polymerization and/or curing prior to exposing to the curingcondition. Commonly used inhibitors, such as radical inhibitors, arecontemplated.

Commonly used surfactants, dispersants, colorants and stabilizers arecontemplated. Exemplary concentrations of each component, if present,range from about 0.01 to about 1, or from about 0.01 to about 0.5, orfrom about 0.01 to about 0.1, weight percent, of the total weight of theformulation containing same.

Exemplary Formulations:

In some of any of the embodiments described herein, the elastomericcurable material is a UV curable material, and in some embodiments, itis an elastomeric (meth)acrylate, for example, an elastomeric acrylate.

In some of any of the embodiments described herein, an additionalcurable component is included in the modeling material formulation, andin some embodiments, this component is a UV-curable acrylate ormethacrylate.

In some of any of the embodiments described herein, the silica particlesare (meth)acrylate-functionalized silica particles.

In some of any of the embodiments described herein, the one or moremodeling material formulation(s) comprise(s) one or more mono-functionalelastomeric acrylate, one or more multi-functional elastomeric acrylate,one or more mono-functional acrylate or methacrylate and one or moremulti-functional acrylate or methacrylate.

In some of these embodiments, the one or more modeling materialformulations further comprise one or more photoinitiators, for example,of the Igracure® family.

In some of any of the embodiments described herein, all curablematerials and the silica particles are included in a single modelingmaterial formulation. In these embodiments, the modeling materialformulation forms a formulation system consisting of one modelingmaterial formulation.

In some of any of the embodiments described herein, the (uncured)building material comprises two or more modeling material formulations.In these embodiments, the modeling material formulation forms aformulation system that comprises two or more modeling materialformulations.

In some of these embodiments, one modeling material formulation (e.g., afirst formulation, or Part A) comprises an elastomeric curable material(e.g., an elastomeric acrylate) and another modeling materialformulation (e.g., a second formulation, or Part B) comprises anadditional curable material.

Alternatively, each of the two modeling material formulations comprisesan elastomeric curable material and one of the formulations furthercomprises an additional curable material.

Further alternatively, each of the two modeling material formulationscomprises an elastomeric curable material, yet, the elastomericmaterials are different in each formulation. For example, oneformulation comprises a mono-functional elastomeric curable material andanother formulation comprises a multi-functional elastomeric material.Alternatively, one formulation comprises a mixture of mono-functionaland multi-functional elastomeric curable materials at a ratio W andanother formulation comprises a mixture of mono-functional andmulti-functional elastomeric curable materials at a ratio Q, wherein Wand Q are different.

Whenever each of the modeling material formulations comprises anelastomeric material as described herein, one or more of the modelingmaterial formulations can further comprise an additional curablematerial. In exemplary embodiments, one of the formulations comprises amono-functional additional material and another comprises amulti-functional additional material. In further exemplary embodiments,one of the formulations comprises an oligomeric curable material andanother formulation comprises a monomeric curable material.

Any combination of elastomeric and additional curable materials asdescribed herein is contemplated for inclusion in the two or moremodeling material formulations. Selecting the composition of themodeling material formulations and the printing mode allows fabricationof objects featuring a variety of properties in a controllable manner,as is described in further detail hereinbelow.

In some embodiments, the one or more modeling material formulations areselected such that a ratio of an elastomeric curable material and anadditional curable material provides a rubbery-like material featuring acertain Shore A hardness.

In some embodiments, a series of modeling material formulations or ofmodeling material formulation systems (e.g., of two or more modelingmaterial formulations) provides for a series of rubbery-like materialsfeaturing a series of Shore A hardness values.

In some embodiments, silica particles, one or more photoinitiators, andoptionally other components, are included in one or both modelingmaterial formulations.

In exemplary modeling material formulations according to some of any ofthe embodiments described herein, all curable materials are(meth)acrylates.

In any of the exemplary modeling material formulations described herein,a concentration of a photoinitiator ranges from about 1% to about 5% byweight, or from about 2% to about 5%, or from about 3% to about 5%, orfrom about 3% to about 4% (e.g., 3, 3.1, 3.2, 3.25, 3.3, 3.4, 3.5, 3.6,3.7, 3.8, 3.85, 3.9, including any intermediate value therebetween) %,by weight, of the total weight of the formulation or formulation systemcomprising same.

In any of the exemplary modeling material formulations described herein,a concentration of an inhibitor ranges from 0 to about 2% weight, orfrom 0 to about 1%, and is, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.7, 0.8, 0.9 or about 1%, by weight, including any intermediatevalue therebetween, of the total weight of the formulation or aformulation system comprising same.

In any of the exemplary modeling material formulations described herein,a concentration of a surfactant ranges from 0 to about 1% weight, andis, for example, 0, 0.01, 0.05, 0.1, 0.5 or about 1%, by weight,including any intermediate value therebetween, of the total weight ofthe formulation or formulation system comprising same.

In any of the exemplary modeling material formulations described herein,a concentration of a dispersant ranges from 0 to about 2% weight, andis, for example, 0, 0.1, 0.5, 0.7, 1, 1.2, 1.3, 1.35, 1.4, 1.5, 1.7, 1.8or about 2%, by weight, including any intermediate value therebetween,of the total weight of the formulation or formulation system comprisingsame.

In exemplary modeling material formulations according to some of any ofthe embodiments described herein, a total concentration of anelastomeric curable material ranges from about 30% to about 90% byweight, or from about 40% to about 90%, by weight, or from about 40% toabout 85%, by weight.

By “total concentration” it is meant herein throughout a total weight inall of the (one or more) modeling material formulations, or in aformulation system as described herein.

In some embodiments, the elastomeric curable material comprises amono-functional elastomeric curable material and a multi-functionalelastomeric curable material.

In some embodiments, a total concentration of the mono-functionalelastomeric curable material ranges from about 20% to about 70%, or fromabout 30% to about 50%, by weight, including any intermediate value andsubranges therebetween. In exemplary embodiments, a total concentrationof the mono-functional elastomeric curable material ranges from about50% to about 70%, or from about 55% to about 65%, or from about 55% toabout 60% (e.g. 58%), by weight, including any intermediate value andsubranges therebetween. In exemplary embodiments, a total concentrationof the mono-functional elastomeric curable material ranges from about30% to about 50%, or from about 35% to about 50%, or from about 40% toabout 45% (e.g., 42%), by weight, including any intermediate value andsubranges therebetween.

In some embodiments, a total concentration of the multi-functionalelastomeric curable material ranges from about 10% to about 30%, byweight. In exemplary embodiments, a concentration of the mono-functionalelastomeric curable material ranges from about 10% to about 20%, or fromabout 10% to about 15% (e.g. 12%), by weight. In exemplary embodiments,a concentration of the mono-functional elastomeric curable materialranges from about 10% to about 30%, or from about 10% to about 20%, orfrom about 15% to about 20% (e.g., 16%), by weight.

In exemplary modeling material formulations according to some of any ofthe embodiments described herein, a total concentration of an additionalcurable material ranges from about 10% to about 40% by weight, or fromabout 15% to about 35%, by weight, including any intermediate value andsubranges therebetween.

In some embodiments, the additional curable material comprises amono-functional curable material.

In some embodiments, a total concentration of the mono-functionaladditional curable material ranges from about 15% to about 25%, or fromabout 20% to about 25% (e.g., 21%), by weight, including anyintermediate value and subranges therebetween. In exemplary embodiments,a concentration of the mono-functional elastomeric curable materialranges from about 20% to about 30%, or from about 25% to about 30%(e.g., 28%), by weight, including any intermediate value and subrangestherebetween.

In exemplary modeling material formulations or formulation systemsaccording to some of any of the embodiments described herein, theelastomeric curable material comprises a mono-functional elastomericcurable material and a multi-functional elastomeric curable material; atotal concentration of the mono-functional elastomeric curable materialranges from about 30% to about 50% (e.g., from about 40% to about 45%)or from about 50% to about 70% (e.g., from about 55% to about 60%) byweight; and a total concentration of the multi-functional elastomericcurable material ranges from about 10% to about 20% by weight; and theone or more formulation(s) further comprise(s) an additionalmono-functional curable material at a total concentration that rangesfrom about 20% to about 30%, by weight.

According to some of any of the embodiments described herein, the one ormore modeling formulation(s) comprise(s) at least one elastomericmono-functional curable material, at least one elastomericmulti-functional curable material and at least additionalmono-functional curable material.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 10% to30%, by weight of the total weight of the one or more modelingformulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric mono-functional curable material rangesfrom 50% to 70%, by weight, of the total weight of the one or moremodeling formulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 20%, by weight, of the total weight of the one ormore modeling formulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 10% to30%, by weight; a total concentration of the elastomeric mono-functionalcurable material ranges from 50% to 70%, by weight; and a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 20%, by weight, of the total weight of the one ormore modeling formulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 20% to30%, by weight, of the total weight of the one or more modelingformulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric mono-functional curable material rangesfrom 30% to 50%, by weight, of the total weight of the one or moremodeling formulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 30%, by weight, of the total weight of the one ormore modeling formulation(s).

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 20% to30%, by weight; a total concentration of the elastomeric mono-functionalcurable material ranges from 30% to 50%, by weight; and a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 30%, by weight, of the total weight of the one ormore modeling formulation.

In the exemplary modeling material formulations described herein, aconcentration of each component is provided as its concentration whenone modeling material formulations is used or as its total concentrationin two or more modeling material formulations.

In some embodiments, a modeling material formulation (or the two or moremodeling material formulations) as described herein, is characterized,when hardened, by Tear Resistance of at least 4,000 N/m, or at least4500 N/m or at least 5,000 N/m.

In some embodiments, a modeling material formulation (or the two or moremodeling material formulations) as described herein, is characterized,when hardened, by Tear Resistance higher by at least 500 N/m, or by atleast 700 N/m, or by at least 800 N/m, than that of the same modelingmaterial formulation(s) devoid of said silica particles, when hardened.

In some embodiments, a modeling material formulation (or the two or moremodeling material formulations) as described herein, is characterized,when hardened, by Tensile Strength of at least 2 MPa.

In some embodiments, a modeling material formulation (or the two or moremodeling material formulations) as described herein, is such that anobject consisting of the cured modeling material and featuring twoO-rings and a tube connecting the rings, is characterized by TearResistance under constant elongation of at least one hour, or at leastone day. In some of these embodiments, the object is as depicted inFIGS. 6A-C.

Formulation System and Kit:

In some of any of the embodiments described herein, there is provided aformulation system which comprises an elastomeric curable material(s) asdescribed herein in any of the respective embodiments, and silicaparticles, as described herein in any of the respective embodiments.

The formulation system can comprise one formulation, or two or moreformulations.

In some embodiments, the formulation system is usable, or is for use, inadditive manufacturing as described herein in any of the respectiveembodiments, for example, as a modeling material formulation system.

The one or more formulations composing the formulation system of thepresent embodiments are each as described herein for the one or moremodeling material formulations, in any of the respective embodiments asany combination thereof.

According to some of any of the embodiments described herein, an amountof the silica particles in the formulation system ranges from 1 to 20,or from 1 to 15, or from 1 to 10, weight percent, of the total weight ofthe formulation system.

According to some of any of the embodiments described herein, a weightratio of a total weight of the elastomeric curable material and a totalweight of the silica particles, in the formulation system, ranges from30:1 to 4:1.

According to some of any of the embodiments described herein, an amountof the elastomeric curable material in the formulation system is atleast 40%, or at least 50%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, theelastomeric curable material is selected from a mono-functionalelastomeric curable monomer, a mono-functional elastomeric curableoligomer, a multi-functional elastomeric curable monomer, amulti-functional elastomeric curable oligomer, and any combinationthereof, as described herein for an elastomeric curable material in anyof the respective embodiments and any combination thereof.

In some embodiments, the elastomeric curable material comprises one ormore materials selected from the materials represented by Formula I, I*,II and III, as described herein in any of the respective embodiments andany combination thereof.

According to some of any of the embodiments described herein, theelastomeric curable material and the silica particles are in the sameformulation.

According to some of any of the embodiments described herein, theformulation system further comprises at least one additional curablematerial.

According to some of any of the embodiments described herein, theadditional curable material is selected from a mono-functional curablemonomer, a mono-functional curable oligomer, a multi-functional curablemonomer, a multi-functional curable oligomer and any combinationthereof, as described herein for an additional curable material in anyof the respective embodiments and any combination thereof.

According to some of any of the embodiments described herein, theelastomeric curable material, the silica particles and the additionalcurable material are in the same formulation.

According to some of any of the embodiments described herein, theformulation system consists of one formulation, and according to someembodiments, this formulation comprises an elastomeric curable material,silica particles and an additional curable material, as described hereinin any of the respective embodiments.

According to some of any of the embodiments described herein, theformulation system comprises two or more formulations.

According to some of any of the embodiments described herein, theformulation system comprises two or more formulations, wherein one ofthe formulations comprises the elastomeric curable material and anotherformulation comprises the additional curable material. Optionally, thetwo or more formulations comprise an elastomeric curable material,silica particles, and optionally an additional curable material, whichare as described herein for two or more modeling material formulations,in any of the respective embodiments and any combination thereof.

According to some of any of the embodiments described herein, theformulation system further comprises at least one additional,non-curable material.

According to some of any of the embodiments described herein, thenon-curable material is selected from a colorant, an initiator, adispersant, a surfactant, a stabilizer, an inhibitor, and anycombination thereof, as described herein for the one or more modelingmaterial formulation, in any of the respective embodiments and anycombination thereof.

According to some of any of the embodiments described herein, theformulation system comprises at least one elastomeric mono-functionalcurable material, at least one elastomeric multi-functional curablematerial and at least additional mono-functional curable material.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 10% to30%, by weight of the total weight of the formulation system.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric mono-functional curable material rangesfrom 50% to 70%, by weight of the total weight of the formulationsystem.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 20%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 10% to30%, by weight; a total concentration of the elastomeric mono-functionalcurable material ranges from 50% to 70%, by weight; and a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 20%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 20% to30%, by weight, of the total weight of the formulation system.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric mono-functional curable material rangesfrom 30% to 50%, by weight, of the total weight of the formulationsystem.

According to some of any of the embodiments described herein, a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 30%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, a totalconcentration of the curable mono-functional material ranges from 20% to30%, by weight; a total concentration of the elastomeric mono-functionalcurable material ranges from 30% to 50%, by weight; and a totalconcentration of the elastomeric multi-functional curable materialranges from 10% to 30%, by weight, of the total weight of theformulation system.

According to some of any of the embodiments described herein, theelastomeric curable material is a UV-curable elastomeric material.

According to some of any of the embodiments described herein, theelastomeric curable material is an acrylic elastomer.

In some embodiments, the formulation system is characterized, whenhardened, by properties as described herein for the one or more modelingmaterial formulations in any of the respective embodiments as anycombination thereof.

In some of any of the embodiments described herein there is provided akit comprising the modeling material formulation(s) or the formulationsystem, as described herein in any of the respective embodiments and anycombination thereof.

In some embodiments, when the kit comprises two or more modelingmaterial formulations, or a formulation system comprising two or moreformulations, each formulation is packaged individually in the kit.

In exemplary embodiments, the formulation(s) are packaged within the kitin a suitable packaging material, preferably, an impermeable material(e.g., water- and gas-impermeable material), and further preferably anopaque material. In some embodiments, the kit further comprisesinstructions to use the formulations in an additive manufacturingprocess, preferably a 3D inkjet printing process as described herein.The kit may further comprise instructions to use the formulations in theprocess in accordance with the method as described herein.

In some embodiments, the kit comprises a series of formulation systems,as described herein in any of the respective embodiments, wherein eachformulation system provides, when hardened, an elastomeric material thatfeatures a certain property, such that the series of formulation systemsprovides a series of elastomeric materials featuring a range of valuesof this property (for example, a series of formulation systems thatprovide a series of Shore A Hardness or a series of Tensile Strength, ora series of Tear Resistance). As described hereinabove, the formulationsystems in the series can differ from one another by the amount and/ortype of silica particles. In some embodiments, each formulation systemis packaged individually within the kit.

The System:

A representative and non-limiting example of a system 110 suitable forAM of an object 112 according to some embodiments of the presentinvention is illustrated in FIG. 1A. System 110 comprises an additivemanufacturing apparatus 114 having a dispensing unit 16 which comprisesa plurality of dispensing heads. Each head preferably comprises an arrayof one or more nozzles 122, as illustrated in FIGS. 2A-C describedbelow, through which a liquid building material 124 is dispensed.

Preferably, but not obligatorily, apparatus 114 is a three-dimensionalinkjet printing apparatus, in which case the dispensing heads are inkjetprinting heads, and the (uncured) building material is dispensed viainkjet technology. This need not necessarily be the case, since, forsome applications, it may not be necessary for the additivemanufacturing apparatus to employ three-dimensional printing techniques.Representative examples of additive manufacturing apparatus contemplatedaccording to various exemplary embodiments of the present inventioninclude, without limitation, fused deposition modeling apparatus andfused material deposition apparatus.

Each dispensing head is optionally and preferably fed via a buildingmaterial reservoir which may optionally include a temperature controlunit (e.g., a temperature sensor and/or a heating device), and amaterial level sensor. To dispense the building material, a voltagesignal is applied to the dispensing heads to selectively depositdroplets of material via the dispensing head nozzles, for example, as inpiezoelectric inkjet printing technology. The dispensing rate of eachhead depends on the number of nozzles, the type of nozzles and theapplied voltage signal rate (frequency). Such dispensing heads are knownto those skilled in the art of solid freeform fabrication.

Preferably, but not obligatorily, the overall number of dispensingnozzles or nozzle arrays is selected such that half of the dispensingnozzles are designated to dispense support material formulation and halfof the dispensing nozzles are designated to dispense modeling materialformulation(s), i.e. the number of nozzles jetting modeling materialformulation(s) is the same as the number of nozzles jetting supportmaterial formulation(s). In the representative example of FIG. 1A, fourdispensing heads 16 a, 16 b, 16 c and 16 d are illustrated. Each ofheads 16 a, 16 b, 16 c and 16 d has a nozzle array. In this Example,heads 16 a and 16 b can be designated for modeling materialformulation(s) and heads 16 c and 16 d can be designated for supportmaterial formulation(s). Thus, head 16 a can dispense a first modelingmaterial formulation, head 16 b can dispense a second modeling materialformulation and heads 16 c and 16 d can both dispense a support materialformulation. In an alternative embodiment, heads 16 c and 16 d, forexample, may be combined in a single head having two nozzle arrays fordepositing a support material formulation.

Yet it is to be understood that it is not intended to limit the scope ofthe present invention and that the number of modeling materialdepositing heads (modeling heads) and the number of support materialdepositing heads (support heads) may differ. Generally, the number ofmodeling heads, the number of support heads and the number of nozzles ineach respective head or head array are selected such as to provide apredetermined ratio, a, between the maximal dispensing rate of thesupport material formulation(s) and the maximal dispensing rate ofmodeling material formulation(s). The value of the predetermined ratio,a, is preferably selected to ensure that in each formed layer, theheight of modeling material equals the height of support material.Typical values for a are from about 0.6 to about 1.5.

For example, for a=1, the overall dispensing rate of support materialformulation is generally the same as the overall dispensing rate of themodeling material formulation(s) when all modeling heads and supportheads operate.

In a preferred embodiment, there are M modeling heads each having marrays of p nozzles, and S support heads each having s arrays of qnozzles such that M×m×p=S×s×q. Each of the M×m modeling arrays and S×ssupport arrays can be manufactured as a separate physical unit, whichcan be assembled and disassembled from the group of arrays. In thisembodiment, each such array optionally and preferably comprises atemperature control unit and a material level sensor of its own, andreceives an individually controlled voltage for its operation.

Apparatus 114 can further comprise a hardening (curing) device 324 whichcan include any device configured to emit light, heat or the like thatmay cause the deposited material to harden (may cause curing). Forexample, hardening device 324 can comprise one or more radiationsources, which can be, for example, an ultraviolet or visible orinfrared lamp, or other sources of electromagnetic radiation, orelectron beam source, depending on the modeling material being used. Insome embodiments of the present invention, hardening device 324 servesfor curing or solidifying the modeling material.

The dispensing head and radiation source are preferably mounted in aframe 128 which is preferably operative to reciprocally move over a tray360, which serves as the working surface. In some embodiments of thepresent invention the radiation sources are mounted on the frame suchthat they follow in the wake of the dispensing heads to at leastpartially cure or solidify the materials just dispensed by thedispensing heads.

Tray 360 is positioned horizontally. According to the common conventionsan X-Y-Z Cartesian coordinate system is selected such that the X-Y planeis parallel to tray 360. Tray 360 is preferably configured to movevertically (along the Z direction), typically downward. In variousexemplary embodiments of the invention, apparatus 114 further comprisesone or more leveling devices 132, e.g. a roller 326. Leveling device 326serves to straighten, level and/or establish a thickness of the newlyformed layer prior to the formation of the successive layer thereon.Leveling device 326 preferably comprises a waste collection device 136for collecting the excess material generated during leveling. Wastecollection device 136 may comprise any mechanism that delivers thematerial to a waste tank or waste cartridge.

In use, the dispensing heads of unit 16 move in a scanning direction,which is referred to herein as the X direction, and selectively dispenseuncured building material in a predetermined configuration in the courseof their passage over tray 360. The building material typicallycomprises one or more types of support material and one or more modelingmaterial formulations. The passage of the dispensing heads of unit 16 isfollowed by the curing of the dispensed modeling material formulation(s)by radiation source 126. In the reverse passage of the heads, back totheir starting point for the layer just deposited, an additionaldispensing of (uncured) building material may be carried out, accordingto predetermined configuration. In the forward and/or reverse passagesof the dispensing heads, the layer thus formed may be straightened byleveling device 326, which preferably follows the path of the dispensingheads in their forward and/or reverse movement. Once the dispensingheads return to their starting point along the X direction, they maymove to another position along an indexing direction, referred to hereinas the Y direction, and continue to build the same layer by reciprocalmovement along the X direction. Alternately, the dispensing heads maymove in the Y direction between forward and reverse movements or aftermore than one forward-reverse movement. The series of scans performed bythe dispensing heads to complete a single layer is referred to herein asa single scan cycle.

Once the layer is completed, tray 360 is lowered in the Z direction to apredetermined Z level, according to the desired thickness of the layersubsequently to be printed. The procedure is repeated to formthree-dimensional object 112 in a layerwise manner.

In another embodiment, tray 360 may be displaced in the Z directionbetween forward and reverse passages of the dispensing head of unit 16,within the layer. Such Z displacement is carried out in order to causecontact of the leveling device with the surface in one direction andprevent contact in the other direction.

System 110 optionally and preferably comprises a building materialsupply system 330 which comprises the building material containers orcartridges and supplies a plurality of building materials to fabricationapparatus 114.

A control unit 152 controls fabrication apparatus 114 and optionally andpreferably also supply system 330. Control unit 152 typically includesan electronic circuit configured to perform the controlling operations.Control unit 152 preferably communicates with a data processor 154 whichtransmits digital data pertaining to fabrication instructions based oncomputer object data, e.g., a CAD configuration represented on acomputer readable medium in a form of a Standard Tessellation Language(STL) format, a StereoLithography Contour (SLC) format, Virtual RealityModeling Language (VRML), Additive Manufacturing File (AMF) format,Drawing Exchange Format (DXF), Polygon File Format (PLY) or any otherformat suitable for Computer-Aided Design (CAD). Typically, control unit152 controls the voltage applied to each dispensing head or nozzle arrayand the temperature of the building material in the respective printinghead.

Once the manufacturing data is loaded to control unit 152 it can operatewithout user intervention. In some embodiments, control unit 152receives additional input from the operator, e.g., using data processor154 or using a user interface 116 communicating with unit 152. Userinterface 116 can be of any type known in the art, such as, but notlimited to, a keyboard, a touch screen and the like. For example,control unit 152 can receive, as additional input, one or more buildingmaterial types and/or attributes, such as, but not limited to, color,characteristic distortion and/or transition temperature, viscosity,electrical property, magnetic property. Other attributes and groups ofattributes are also contemplated.

Another representative and non-limiting example of a system 10 suitablefor AM of an object according to some embodiments of the presentinvention is illustrated in FIGS. 1B-D. FIGS. 1B-D illustrate a top view(FIG. 1B), a side view (FIG. 1C) and an isometric view (FIG. 1D) ofsystem 10.

In the present embodiments, system 10 comprises a tray 12 and aplurality of inkjet printing heads 16, each having a plurality ofseparated nozzles. Tray 12 can have a shape of a disk or it can beannular. Non-round shapes are also contemplated, provided they can berotated about a vertical axis.

Tray 12 and heads 16 are optionally and preferably mounted such as toallow a relative rotary motion between tray 12 and heads 16. This can beachieved by (i) configuring tray 12 to rotate about a vertical axis 14relative to heads 16, (ii) configuring heads 16 to rotate about verticalaxis 14 relative to tray 12, or (iii) configuring both tray 12 and heads16 to rotate about vertical axis 14 but at different rotation velocities(e.g., rotation at opposite direction). While the embodiments below aredescribed with a particular emphasis to configuration (i) wherein thetray is a rotary tray that is configured to rotate about vertical axis14 relative to heads 16, it is to be understood that the presentapplication contemplates also configurations (ii) and (iii). Any one ofthe embodiments described herein can be adjusted to be applicable to anyof configurations (ii) and (iii), and one of ordinary skills in the art,provided with the details described herein, would know how to make suchadjustment.

In the following description, a direction parallel to tray 12 andpointing outwardly from axis 14 is referred to as the radial directionr, a direction parallel to tray 12 and perpendicular to the radialdirection r is referred to herein as the azimuthal direction φ, and adirection perpendicular to tray 12 is referred to herein is the verticaldirection z.

The term “radial position,” as used herein, refers to a position on orabove tray 12 at a specific distance from axis 14. When the term is usedin connection to a printing head, the term refers to a position of thehead which is at specific distance from axis 14. When the term is usedin connection to a point on tray 12, the term corresponds to any pointthat belongs to a locus of points that is a circle whose radius is thespecific distance from axis 14 and whose center is at axis 14.

The term “azimuthal position,” as used herein, refers to a position onor above tray 12 at a specific azimuthal angle relative to apredetermined reference point. Thus, radial position refers to any pointthat belongs to a locus of points that is a straight line forming thespecific azimuthal angle relative to the reference point.

The term “vertical position,” as used herein, refers to a position overa plane that intersect the vertical axis 14 at a specific point.

Tray 12 serves as a supporting structure for three-dimensional printing.The working area on which one or objects are printed is typically, butnot necessarily, smaller than the total area of tray 12. In someembodiments of the present invention the working area is annular. Theworking area is shown at 26. In some embodiments of the presentinvention tray 12 rotates continuously in the same direction throughoutthe formation of object, and in some embodiments of the presentinvention tray reverses the direction of rotation at least once (e.g.,in an oscillatory manner) during the formation of the object. Tray 12 isoptionally and preferably removable. Removing tray 12 can be formaintenance of system 10, or, if desired, for replacing the tray beforeprinting a new object. In some embodiments of the present inventionsystem 10 is provided with one or more different replacement trays(e.g., a kit of replacement trays), wherein two or more trays aredesignated for different types of objects (e.g., different weights)different operation modes (e.g., different rotation speeds), etc. Thereplacement of tray 12 can be manual or automatic, as desired. Whenautomatic replacement is employed, system 10 comprises a trayreplacement device 36 configured for removing tray 12 from its positionbelow heads 16 and replacing it by a replacement tray (not shown). Inthe representative illustration of FIG. 1B tray replacement device 36 isillustrated as a drive 38 with a movable arm 40 configured to pull tray12, but other types of tray replacement devices are also contemplated.

Exemplified embodiments for the printing head 16 are illustrated inFIGS. 2A-2C. These embodiments can be employed for any of the AM systemsdescribed above, including, without limitation, system 110 and system10.

FIGS. 2A-B illustrate a printing head 16 with one (FIG. 2A) and two(FIG. 2B) nozzle arrays 22. The nozzles in the array are preferablyaligned linearly, along a straight line. In embodiments in which aparticular printing head has two or more linear nozzle arrays, thenozzle arrays are optionally and preferably can be parallel to eachother.

When a system similar to system 110 is employed, all printing heads 16are optionally and preferably oriented along the indexing direction withtheir positions along the scanning direction being offset to oneanother.

When a system similar to system 10 is employed, all printing heads 16are optionally and preferably oriented radially (parallel to the radialdirection) with their azimuthal positions being offset to one another.Thus, in these embodiments, the nozzle arrays of different printingheads are not parallel to each other but are rather at an angle to eachother, which angle being approximately equal to the azimuthal offsetbetween the respective heads. For example, one head can be orientedradially and positioned at azimuthal position φ₁, and another head canbe oriented radially and positioned at azimuthal position φ₂. In thisexample, the azimuthal offset between the two heads is φ₁-φ₂, and theangle between the linear nozzle arrays of the two heads is also φ₁-φ₂.

In some embodiments, two or more printing heads can be assembled to ablock of printing heads, in which case the printing heads of the blockare typically parallel to each other. A block including several inkjetprinting heads 16 a, 16 b, 16 c is illustrated in FIG. 2C.

In some embodiments, system 10 comprises a support structure 30positioned below heads 16 such that tray 12 is between support structure30 and heads 16. Support structure 30 may serve for preventing orreducing vibrations of tray 12 that may occur while inkjet printingheads 16 operate. In configurations in which printing heads 16 rotateabout axis 14, support structure 30 preferably also rotates such thatsupport structure 30 is always directly below heads 16 (with tray 12between heads 16 and tray 12).

Tray 12 and/or printing heads 16 is optionally and preferably configuredto move along the vertical direction z, parallel to vertical axis 14 soas to vary the vertical distance between tray 12 and printing heads 16.In configurations in which the vertical distance is varied by movingtray 12 along the vertical direction, support structure 30 preferablyalso moves vertically together with tray 12. In configurations in whichthe vertical distance is varied by heads 16 along the verticaldirection, while maintaining the vertical position of tray 12 fixed,support structure 30 is also maintained at a fixed vertical position.

The vertical motion can be established by a vertical drive 28. Once alayer is completed, the vertical distance between tray 12 and heads 16can be increased (e.g., tray 12 is lowered relative to heads 16) by apredetermined vertical step, according to the desired thickness of thelayer subsequently to be printed. The procedure is repeated to form athree-dimensional object in a layerwise manner.

The operation of inkjet printing heads 16 and optionally and preferablyalso of one or more other components of system 10, e.g., the motion oftray 12, are controlled by a controller 20. The controller can has anelectronic circuit and a non-volatile memory medium readable by thecircuit, wherein the memory medium stores program instructions which,when read by the circuit, cause the circuit to perform controloperations as further detailed below.

Controller 20 can also communicate with a host computer 24 whichtransmits digital data pertaining to fabrication instructions based oncomputer object data, e.g., in a form of STL, SLC format, VRML, AMFformat, DXF, PLY or any other format suitable for CAD. The object dataformats are typically structured according to a Cartesian system ofcoordinates. In these cases, computer 24 preferably executes a procedurefor transforming the coordinates of each slice in the computer objectdata from a Cartesian system of coordinates into a polar system ofcoordinates. Computer 24 optionally and preferably transmits thefabrication instructions in terms of the transformed system ofcoordinates. Alternatively, computer 24 can transmit the fabricationinstructions in terms of the original system of coordinates as providedby the computer object data, in which case the transformation ofcoordinates is executed by the circuit of controller 20.

The transformation of coordinates allows three-dimensional printing overa rotating tray. In conventional three-dimensional printing, theprinting heads reciprocally move above a stationary tray along straightlines. In such conventional systems, the printing resolution is the sameat any point over the tray, provided the dispensing rates of the headsare uniform. Unlike conventional three-dimensional printing, not all thenozzles of the head points cover the same distance over tray 12 duringat the same time. The transformation of coordinates is optionally andpreferably executed so as to ensure equal amounts of excess material atdifferent radial positions.

Typically, the controller 152 or 20 controls the voltage applied to therespective component of the system 10 based on the fabricationinstructions and based on the stored program instructions as describedbelow.

Generally, controller 152 or 20 controls printing heads 16 to dispense,during the rotation of tray 360 or 12, droplets of building material inlayers, such as to print a three-dimensional object on tray 360 or 12.

System 10 or 110 optionally and preferably comprises one or moreradiation sources 18, which provides curing energy and which can be, forexample, an ultraviolet or visible or infrared lamp, or other sources ofelectromagnetic radiation, or electron beam source, depending on themodeling material formulation being used. Radiation source can includeany type of radiation emitting device, including, without limitation,light emitting diode (LED), digital light processing (DLP) system,resistive lamp and the like. Radiation source 18 serves for curing orsolidifying the modeling material. In various exemplary embodiments ofthe invention the operation of radiation source 18 is controlled bycontroller 20 which may activate and deactivate radiation source 18 andmay optionally also control the amount of radiation generated byradiation source 18.

In some embodiments of the invention, system 10 further comprises one ormore leveling devices 32 which can be manufactured as a roller or ablade. Leveling device 32 serves to straighten the newly formed layerprior to the formation of the successive layer thereon. In someembodiments, leveling device 32 has the shape of a conical rollerpositioned such that its symmetry axis 34 is tilted relative to thesurface of tray 12 and its surface is parallel to the surface of thetray. This embodiment is illustrated in the side view of system 10 (FIG.1C).

The conical roller can have the shape of a cone or a conical frustum.

The opening angle of the conical roller is preferably selected such thatis a constant ratio between the radius of the cone at any location alongits axis 34 and the distance between that location and axis 14. Thisembodiment allows roller 32 to efficiently level the layers, since whilethe roller rotates, any point p on the surface of the roller has alinear velocity which is proportional (e.g., the same) to the linearvelocity of the tray at a point vertically beneath point p. In someembodiments, the roller has a shape of a conical frustum having a heighth, a radius R₁ at its closest distance from axis 14, and a radius R₂ atits farthest distance from axis 14, wherein the parameters h, R₁ and R₂satisfy the relation R₁/R₂=(R−h)/h and wherein R is the farthestdistance of the roller from axis 14 (for example, R can be the radius oftray 12).

The operation of leveling device 32 is optionally and preferablycontrolled by controller 20 which may activate and deactivate levelingdevice 32 and may optionally also control its position along a verticaldirection (parallel to axis 14) and/or a radial direction (parallel totray 12 and pointing toward or away from axis 14.

In some embodiments of the present invention printing heads 16 of system10 are configured to reciprocally move relative to tray along the radialdirection r. These embodiments are useful when the lengths of the nozzlearrays 22 of heads 16 are shorter than the width along the radialdirection of the working area 26 on tray 12. The motion of heads 16along the radial direction is optionally and preferably controlled bycontroller 20.

Further details on the principles and operations of an AM systemsuitable for the present embodiments are found in U.S. PublishedApplication No. 20100191360, the contents of which are herebyincorporated by reference.

The Method:

FIG. 3 presents a flowchart describing an exemplary method according tosome embodiments of the present invention.

It is to be understood that, unless otherwise defined, the operationsdescribed hereinbelow can be executed either contemporaneously orsequentially in many combinations or orders of execution. Specifically,the ordering of the flowchart diagrams is not to be considered aslimiting. For example, two or more operations, appearing in thefollowing description or in the flowchart diagrams in a particularorder, can be executed in a different order (e.g., a reverse order) orsubstantially contemporaneously. Additionally, several operationsdescribed below are optional and may not be executed.

Computer programs implementing the method of the present embodiments cancommonly be distributed to users on a distribution medium such as, butnot limited to, a floppy disk, a CD-ROM, a flash memory device and aportable hard drive. From the distribution medium, the computer programscan be copied to a hard disk or a similar intermediate storage medium.The computer programs can be run by loading the computer instructionseither from their distribution medium or their intermediate storagemedium into the execution memory of the computer, configuring thecomputer to act in accordance with the method of this invention. Allthese operations are well-known to those skilled in the art of computersystems.

The computer implemented method of the present embodiments can beembodied in many forms. For example, it can be embodied in on a tangiblemedium such as a computer for performing the method operations. It canbe embodied on a computer readable medium, comprising computer readableinstructions for carrying out the method operations. In can also beembodied in electronic device having digital computer capabilitiesarranged to run the computer program on the tangible medium or executethe instruction on a computer readable medium.

The method begins at 200 and optionally and preferably continues to 201at which computer object data (e.g., 3D printing data) corresponding tothe shape of the object are received. The data can be received, forexample, from a host computer which transmits digital data pertaining tofabrication instructions based on computer object data, e.g., in a formof STL, SLC format, VRML, AMF format, DXF, PLY or any other formatsuitable for CAD.

The method continues to 202 at which droplets of the uncured buildingmaterial as described herein (e.g., one or more modeling materialformulations as described herein and optionally a support materialformulation) are dispensed in layers, on a receiving medium, optionallyand preferably using an AM system, such as, but not limited to, system110 or system 10, according to the computer object data (e.g., printingdata), and as described herein. In any of the embodiments describedherein the dispensing 202 is by at least two different multi-nozzleinkjet printing heads The receiving medium can be a tray of an AM system(e.g., tray 360 or 12) as described herein or a previously depositedlayer.

In some embodiments of the present invention, the dispensing 202 iseffected under ambient environment.

Optionally, before being dispensed, the uncured building material, or apart thereof (e.g., one or more formulations of the building material),is heated, prior to being dispensed. These embodiments are particularlyuseful for uncured building material formulations having relatively highviscosity at the operation temperature of the working chamber of a 3Dinkjet printing system. The heating of the formulation(s) is preferablyto a temperature that allows jetting the respective formulation througha nozzle of a printing head of a 3D inkjet printing system. In someembodiments of the present invention, the heating is to a temperature atwhich the respective formulation exhibits a viscosity of no more than Xcentipoises, where X is about 30 centipoises, preferably about 25centipoises and more preferably about 20 centipoises, or 18 centipoises,or 16 centipoises, or 14 centipoises, or 12 centipoises, or 10centipoises, or even lower.

The heating can be executed before loading the respective formulationinto the printing head of the AM (e.g., 3D inkjet printing) system, orwhile the formulation is in the printing head or while the compositionpasses through the nozzle of the printing head.

In some embodiments, the heating is executed before loading of therespective formulation into the dispensing (e.g., inkjet printing) head,so as to avoid clogging of the dispensing (e.g., inkjet printing) headby the formulation in case its viscosity is too high.

In some embodiments, the heating is executed by heating the dispensing(e.g., inkjet printing) heads, at least while passing the modelingmaterial formulation(s) through the nozzle of the dispensing (e.g.,inkjet printing) head.

Once the uncured building material is dispensed on the receiving mediumaccording to the computer object data (e.g., printing data), the methodoptionally and preferably continues to 203 at which curing energy isapplied to the deposited layers, e.g., by means of a radiation source asdescribed herein. Preferably, the curing is applied to each individuallayer following the deposition of the layer and prior to the depositionof the previous layer.

In some embodiments, applying a curing energy is effected under agenerally dry and inert environment, as described herein.

The method ends at 204.

In some embodiments, the method is executed using an exemplary system asdescribed herein in any of the respective embodiments and anycombination thereof.

The modeling material formulation(s) can be contained in a particularcontainer or cartridge of a solid freeform fabrication apparatus or acombination of modeling material formulations deposited from differentcontainers of the apparatus.

In some embodiments, at least one, or at least a few (e.g., at least 10,at least 20, at least 30 at least 40, at least 50, at least 60, at least80, or more), or all, of the layers is/are formed by dispensingdroplets, as in 202, of a single modeling material formulation, asdescribed herein in any of the respective embodiments.

In some embodiments, at least one, or at least a few (e.g., at least 10,at least 20, at least 30 at least 40, at least 50, at least 60, at least80, or more), or all, of the layers is/are formed by dispensingdroplets, as in 202, of two or more modeling material formulations, asdescribed herein in any of the respective embodiments, each from adifferent dispensing (e.g., inkjet printing) head.

These embodiments provide, inter alia, the ability to select materialsfrom a given number of materials and define desired combinations of theselected materials and their properties. According to the presentembodiments, the spatial locations of the deposition of each materialwith the layer is defined, either to effect occupation of differentthree-dimensional spatial locations by different materials, or to effectoccupation of substantially the same three-dimensional location oradjacent three-dimensional locations by two or more different materialsso as to allow post deposition spatial combination of the materialswithin the layer, thereby to form a composite material at the respectivelocation or locations.

Any post deposition combination or mix of modeling materials iscontemplated. For example, once a certain material is dispensed it maypreserve its original properties. However, when it is dispensedsimultaneously with another modeling material or other dispensedmaterials which are dispensed at the same or nearby locations, acomposite material having a different property or properties to thedispensed materials is formed.

Some of the embodiments thus enable the deposition of a broad range ofmaterial combinations, and the fabrication of an object which mayconsist of multiple different combinations of materials, in differentparts of the object, according to the properties desired to characterizeeach part of the object.

In some of these embodiments, the two or more modeling materialformulations are dispensed in a voxelated manner, wherein voxels of oneof said modeling material formulations are interlaced with voxels of atleast one another modeling material formulation.

Some embodiments thus provide a method of layerwise fabrication of athree-dimensional object, in which for each of at least a few (e.g., atleast two or at least three or at least 10 or at least 20 or at least 40or at least 80) of the layers or all the layers, two or more modelingformulations are dispensed, optionally and preferably using system 10 orsystem 110. Each modeling formulation is preferably dispensed by jettingit out of a plurality of nozzles of a printing head (e.g., head 16). Thedispensing is in a voxelated manner, wherein voxels of one of saidmodeling material formulations are interlaced with voxels of at leastone another modeling material formulation, according to a predeterminedvoxel ratio.

Such a combination of two modeling material formulations at apredetermined voxel ratio is referred to as digital material (DM). Arepresentative example of a digital material is illustrated in FIG. 4,showing materials A and B which are interlaced over a region of a layerin a voxelated manner.

In some embodiments, dispensing two modeling material formulations at apredetermined voxel ratio allows obtaining rubbery-like materialsfeaturing mechanical properties as desired. For example, by manipulatingthe voxel ratio, a series of rubbery-like digital material featuringvarious Shore A hardness values can be obtained, in a controllabledigital manner.

For any predetermined ratio of the materials, a digital material can beformed for example, by ordered or random interlacing. Also contemplatedare embodiments in which the interlacing is semi-random, for example, arepetitive pattern of sub-regions wherein each sub-region comprisesrandom interlacing.

In some of any of the embodiments described herein, when droplets of twoor more modeling material formulations are dispensed, in each of atleast a few layers, as described herein, the dispensing is such thatforms a core region and one or more envelope regions at least partiallysurrounding said core region. Such a dispensing results in fabricationof an object constructed from a plurality of layers and a layered coreconstituting core regions and a layered shell constituting enveloperegions.

The structure according to some of these embodiments is a shelledstructure made of two or more curable materials. The structure typicallycomprises a layered core which is at least partially coated by one ormore layered shells such that at least one layer of the core engages thesame plane with a layer of at least one of the shells. The thickness ofeach shell, as measured perpendicularly to the surface of the structure,is typically at least 10 μm. In various exemplary embodiments, the coreand the shell are different from each other in their thermo-mechanicalproperties. This is readily achieved by fabricating the core and shellfrom different modeling material formulations or different combinationsof modeling material formulations. The thermo-mechanical properties ofthe core and shell are referred to herein as “core thermo-mechanicalproperties” and “shell thermo-mechanical properties,” respectively.

A representative and non-limiting example of a structure according tosome embodiments of the present invention is shown in FIGS. 5A-D.

FIG. 5A is a schematic illustration of a perspective view a structure60, and FIG. 5B is a cross-sectional view of structure 60 along line A-Aof FIG. 5A. For clarity of presentation a Cartesian coordinate system isalso illustrated.

Structure 60 comprises a plurality of layers 62 stacked along the zdirection. Structure 60 is typically fabricated by an AM technique,e.g., using system 10 or 110, whereby the layers are formed in asequential manner. Thus, the z direction is also referred to herein asthe “build direction” of the structure. Layers 62 are, therefore,perpendicular to the build direction. Although structure 60 is shown asa cylinder, this need not necessarily be the case, since the structureof the present embodiments can have any shape.

The shell and core of structure 60 are shown at 64 and 66, respectively.As shown, the layers of core 66 and the layers of shell 64 areco-planar. The AM technique allows the simultaneous fabrication of shell64 and core 66, whereby for a particular formed layer, the inner part ofthe layer constitutes a layer of the core, and the periphery of thelayer, or part thereof, constitutes a layer of the shell.

A peripheral section of a layer which contributes to shell 64 isreferred to herein as an “envelope region” of the layer. In thenon-limiting example of FIGS. 5A and 5B, each of layers 62 has anenvelope region. Namely, each layer in FIGS. 5A and 2B contributes bothto the core and to the shell. However, this need not necessarily be thecase, since, for some applications, it may be desired to have the coreexposed to the environment in some regions. In these applications, atleast some of the layers do not include an envelope region. Arepresentative example of such configuration is illustrated in thecross-sectional view of FIG. 5C, showing some layers 68 which contributeto the core but not to the shell, and some layers 70 which contribute toboth the core and the shell. In some embodiments, one or more layers donot include a region with core thermo-mechanical properties and compriseonly a region with shell thermo-mechanical properties. These embodimentsare particularly useful when the structure has one or more thin parts,wherein the layers forming those parts of the structure are preferablydevoid of a core region. Also contemplated are embodiments in which oneor more layers do not include a region with shell thermo-mechanicalproperties and comprise only a region with core thermo-mechanicalproperties.

The shell can, optionally and preferably, also cover structure 60 fromabove and/or below, relative to the z direction. In these embodiments,some layers at the top most and/or bottom most parts of structure 60have at least one material property which is different from core 66. Invarious exemplary embodiments of the invention the top most and/orbottom most parts of structure 60 have the same material property asshell 64. A representative example of this embodiment is illustrated inFIG. 5D. The top/bottom shell of structure 60 may be thinner (e.g., 2times thinner) than the side shell, e.g. when the top or bottom shellcomprises a layer above or below the structure, and therefore has thesame thickness as required for layers forming the object.

In some embodiments of the present invention both the core and the shellare rubber-like materials.

In some embodiments of the present invention both the core and the shellare DM materials.

When both the core and shell are made of a DM composed of the samemodeling material formulations, the relative surface density of any ofthe modeling materials in the core is different from the relativesurface density of that material in the shell or envelope region. Insome embodiments, however, the core is formed from a DM and the shell isformed of a single modeling material formulation or vice versa.

In various exemplary embodiments of the invention the thickness of theshell, as measured in the x-y plane (perpendicularly to the builddirection z) is non-uniform across the build direction. In other words,different layers of the structure may have envelope regions of differentwidths. For example, the thickness of the shell along a directionparallel to the x-y plane can be calculated as a percentage of thediameter of the respective layer along that direction, thus making thethickness dependent on the size of the layer. In various exemplaryembodiments of the invention the thickness of the shell is non-uniformacross a direction which is tangential to the outer surface of the shelland perpendicular to the build direction. In terms of the structure'slayers, these embodiments correspond to an envelope region having awidth which is non-uniform along the periphery of the respective layer.

In some embodiments of the present invention the shell of the structure,or part thereof, is by itself a ‘shelled’ structure, comprising morethan envelope region. Specifically in these embodiments, the structurecomprises an inner core, at least partially surrounded by at least oneintermediate envelope region, wherein the intermediate envelope(s) issurrounded by an outer envelope region. The thickness of theintermediate envelope region(s), as measured perpendicularly to thebuild direction, is optionally and preferably larger (e.g., 10 timeslarger) than the thickness of the outermost envelope region. In theseembodiments, the intermediate envelope region(s) serves as a shell ofthe structure and therefore has the properties of the shell as furtherdetailed hereinabove. The outermost envelope shell may also serve forprotecting the intermediate envelope(s) from breakage under load.

The structure of the present embodiments can be formed, as stated, in alayerwise manner, for example, using system 10 or 110 described above.In various exemplary embodiments of the invention a computer implementedmethod automatically performs dynamic adaptation of the shell to thespecific elements of the structure. The method can optionally andpreferably employ user input to calculate the shell for each region ofthe structure and assigns the voxels of the outer surfaces to therespective modeling material or combination of modeling materials. Thecomputer implemented method can be executed by a control unit whichcontrols the solid freeform fabrication apparatus (e.g., control unit152 or 20 see FIGS. 1A and 1B) via a data processor (e.g., dataprocessor 154 or 24).

In some embodiments of the present invention one or more additionalshell layers are dispensed so as to form a shell also at the top mostand/or bottom most parts of the structure. These layers are preferablydevoid of a core region since they serve for shelling the core fromabove or from below. When it is desired to shell the core from above,the additional shell layer(s) are dispensed on top of all other layers,and when it is desired to shell the core from below, the additionallayer(s) are dispensed on the working surface (e.g., tray 360 or 12, seeFIGS. 1A and 1B) while all other layers are dispensed thereafter.

Any of the envelope regions optionally has a width of at least 10 μm.Preferably, all the envelope regions have a width of at least 10 μm.

Any of the core and envelope regions, and optionally also the top mostand/or bottom most additional layers, may be fabricated using modelingmaterial formulations or combinations of modeling material formulations(e.g., digital materials) as described herein.

In some embodiments of this invention, the shell is fabricatedselectively in different regions of the structure so as to change thematerial properties only in selected regions areas without affecting themechanical properties of other regions.

In some of any of the embodiments of the present invention, once thelayers are dispensed as described herein, exposure to curing energy asdescribed herein is effected. In some embodiments, the curable materialsare UV-curable materials and the curing energy is such that theradiation source emits UV radiation.

In some embodiments, where the building material comprises also supportmaterial formulation(s), the method proceeds to removing the supportmaterial formulation. This can be performed by mechanical and/orchemical means, as would be recognized by any person skilled in the art.

The Object:

Embodiments of the present invention provide three-dimensional objectscomprising in at least a portion thereof an elastomeric material.

When the object is made of a single modeling material formulation, asdescribed herein, it features mechanical properties as described hereinfor a modeling material formulation, when hardened (cured).

In some embodiments, the object is made of two of more modeling materialformulations, and in some of these embodiments, at least a portion ofthe object is made of digital materials, as described herein. In someembodiments, the object comprises a core-shell structure as describedherein in any of the respective embodiments, and features properties inaccordance with the selected materials and structure.

In some embodiments, the object is made of different elastomericmaterials at different portions thereof (e.g., two or more portionsthereof), and each of these portion features a different property (forexample, a different Shore A Hardness, a different Modulus, etc.), asdesired.

It is expected that during the life of a patent maturing from thisapplication many relevant elastomeric curable materials, other curablematerials and silica particles will be developed and the scope of theterms “elastomeric curable material”, “curable material” and “silicaparticles” is intended to include all such new technologies a priori.

As used herein the term “about” refers to ±10% or ±5%.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

Herein throughout, the term “(meth)acrylic” encompasses acrylic andmethacrylic compounds.

Herein throughout, the phrase “linking moiety” or “linking group”describes a group that connects two or more moieties or groups in acompound. A linking moiety is typically derived from a bi- ortri-functional compound, and can be regarded as a bi- or tri-radicalmoiety, which is connected to two or three other moieties, via two orthree atoms thereof, respectively.

Exemplary linking moieties include a hydrocarbon moiety or chain,optionally interrupted by one or more heteroatoms, as defined herein,and/or any of the chemical groups listed below, when defined as linkinggroups.

When a chemical group is referred to herein as “end group” it is to beinterpreted as a substituent, which is connected to another group viaone atom thereof.

Herein throughout, the term “hydrocarbon” collectively describes achemical group composed mainly of carbon and hydrogen atoms. Ahydrocarbon can be comprised of alkyl, alkene, alkyne, aryl, and/orcycloalkyl, each can be substituted or unsubstituted, and can beinterrupted by one or more heteroatoms. The number of carbon atoms canrange from 2 to 20, and is preferably lower, e.g., from 1 to 10, or from1 to 6, or from 1 to 4. A hydrocarbon can be a linking group or an endgroup.

Bisphenol A is an example of a hydrocarbon comprised of 2 aryl groupsand one alkyl group.

As used herein, the term “amine” describes both a —NR′R″ group and a—NR′— group, wherein R′ and R″ are each independently hydrogen, alkyl,cycloalkyl, aryl, as these terms are defined hereinbelow.

The amine group can therefore be a primary amine, where both R′ and R″are hydrogen, a secondary amine, where R′ is hydrogen and R″ is alkyl,cycloalkyl or aryl, or a tertiary amine, where each of R′ and R″ isindependently alkyl, cycloalkyl or aryl.

Alternatively, R′ and R″ can each independently be hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, carbonyl, C-carboxylate, O-carboxylate,N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate,O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine.

The term “amine” is used herein to describe a —NR′R″ group in caseswhere the amine is an end group, as defined hereinunder, and is usedherein to describe a —NR′— group in cases where the amine is a linkinggroup or is or part of a linking moiety.

The term “alkyl” describes a saturated aliphatic hydrocarbon includingstraight chain and branched chain groups. Preferably, the alkyl grouphas 1 to 30, or 1 to 20 carbon atoms. Whenever a numerical range; e.g.,“1-20”, is stated herein, it implies that the group, in this case thealkyl group, may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms,etc., up to and including 20 carbon atoms. The alkyl group may besubstituted or unsubstituted. Substituted alkyl may have one or moresubstituents, whereby each substituent group can independently be, forexample, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl,heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine.

The alkyl group can be an end group, as this phrase is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this phrase is defined hereinabove, which connects twoor more moieties via at least two carbons in its chain. When the alkylis a linking group, it is also referred to herein as “alkylene” or“alkylene chain”.

Herein, a C(1-4) alkyl, substituted by a hydrophilic group, as definedherein, is included under the phrase “hydrophilic group” herein.

Alkene and Alkyne, as used herein, are an alkyl, as defined herein,which contains one or more double bond or triple bond, respectively.

The term “cycloalkyl” describes an all-carbon monocyclic ring or fusedrings (i.e., rings which share an adjacent pair of carbon atoms) groupwhere one or more of the rings does not have a completely conjugatedpi-electron system. Examples include, without limitation, cyclohexane,adamantine, norbornyl, isobornyl, and the like. The cycloalkyl group maybe substituted or unsubstituted. Substituted cycloalkyl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The cycloalkyl group can be an end group, as this phrase isdefined hereinabove, wherein it is attached to a single adjacent atom,or a linking group, as this phrase is defined hereinabove, connectingtwo or more moieties at two or more positions thereof.

Cycloalkyls of 1-6 carbon atoms, substituted by two or more hydrophilicgroups, as defined herein, is included under the phrase “hydrophilicgroup” herein.

The term “heteroalicyclic” describes a monocyclic or fused ring grouphaving in the ring(s) one or more atoms such as nitrogen, oxygen andsulfur. The rings may also have one or more double bonds. However, therings do not have a completely conjugated pi-electron system.Representative examples are piperidine, piperazine, tetrahydrofuran,tetrahydropyrane, morpholino, oxalidine, and the like.

The heteroalicyclic may be substituted or unsubstituted. Substitutedheteroalicyclic may have one or more substituents, whereby eachsubstituent group can independently be, for example, hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate,O-thiocarbamate, urea, thiourea, O-carbamate, N-carbamate, C-amide,N-amide, guanyl, guanidine and hydrazine. The heteroalicyclic group canbe an end group, as this phrase is defined hereinabove, where it isattached to a single adjacent atom, or a linking group, as this phraseis defined hereinabove, connecting two or more moieties at two or morepositions thereof.

A heteroalicyclic group which includes one or more of electron-donatingatoms such as nitrogen and oxygen, and in which a numeral ratio ofcarbon atoms to heteroatoms is 5:1 or lower, is included under thephrase “hydrophilic group” herein.

The term “aryl” describes an all-carbon monocyclic or fused-ringpolycyclic (i.e., rings which share adjacent pairs of carbon atoms)groups having a completely conjugated pi-electron system. The aryl groupmay be substituted or unsubstituted. Substituted aryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The aryl group can be an end group, as this term is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this term is defined hereinabove, connecting two ormore moieties at two or more positions thereof.

The term “heteroaryl” describes a monocyclic or fused ring (i.e., ringswhich share an adjacent pair of atoms) group having in the ring(s) oneor more atoms, such as, for example, nitrogen, oxygen and sulfur and, inaddition, having a completely conjugated pi-electron system. Examples,without limitation, of heteroaryl groups include pyrrole, furan,thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine,quinoline, isoquinoline and purine. The heteroaryl group may besubstituted or unsubstituted. Substituted heteroaryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,O-carbamate, N-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The heteroaryl group can be an end group, as this phrase isdefined hereinabove, where it is attached to a single adjacent atom, ora linking group, as this phrase is defined hereinabove, connecting twoor more moieties at two or more positions thereof. Representativeexamples are pyridine, pyrrole, oxazole, indole, purine and the like.

The term “halide” and “halo” describes fluorine, chlorine, bromine oriodine.

The term “haloalkyl” describes an alkyl group as defined above, furthersubstituted by one or more halide.

The term “sulfate” describes a —O—S(═O)₂—OR′ end group, as this term isdefined hereinabove, or an —O—S(═O)₂—O— linking group, as these phrasesare defined hereinabove, where R′ is as defined hereinabove.

The term “thiosulfate” describes a —O—S(═S)(═O)—OR′ end group or a—O—S(═S)(═O)—O— linking group, as these phrases are defined hereinabove,where R′ is as defined hereinabove.

The term “sulfite” describes an —O—S(═O)—O—R′ end group or a —O—S(═O)—O—group linking group, as these phrases are defined hereinabove, where R′is as defined hereinabove.

The term “thiosulfite” describes a —O—S(═S)—O—R′ end group or an—O—S(═S)—O— group linking group, as these phrases are definedhereinabove, where R′ is as defined hereinabove.

The term “sulfinate” describes a —S(═O)—OR′ end group or an —S(═O)—O—group linking group, as these phrases are defined hereinabove, where R′is as defined hereinabove.

The term “sulfoxide” or “sulfinyl” describes a —S(═O)R′ end group or an—S(═O)— linking group, as these phrases are defined hereinabove, whereR′ is as defined hereinabove.

The term “sulfonate” describes a —S(═O)₂—R′ end group or an —S(═O)₂—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “S-sulfonamide” describes a —S(═O)₂—NR′R″ end group or a—S(═O)₂—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-sulfonamide” describes an R'S(═O)₂—NR″— end group or a—S(═O)₂—NR′— linking group, as these phrases are defined hereinabove,where R′ and R″ are as defined herein.

The term “disulfide” refers to a —S—SR′ end group or a —S—S— linkinggroup, as these phrases are defined hereinabove, where R′ is as definedherein.

The term “phosphonate” describes a —P(═O)(OR′)(OR″) end group or a—P(═O)(OR′)(O)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “thiophosphonate” describes a —P(═S)(OR′)(OR″) end group or a—P(═S)(OR′)(O)— linking group, as these phrases are defined hereinabove,with R′ and

R″ as defined herein.

The term “phosphinyl” describes a —PR′R″ end group or a —PR′— linkinggroup, as these phrases are defined hereinabove, with R′ and R″ asdefined hereinabove.

The term “phosphine oxide” describes a —P(═O)(R′)(R″) end group or a—P(═O)(R′)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “phosphine sulfide” describes a —P(═S)(R′)(R″) end group or a—P(═S)(R′)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “phosphite” describes an —O—PR′(═O)(OR″) end group or an—O—PH(═O)(O)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “carbonyl” or “carbonate” as used herein, describes a —C(═O)—R′end group or a —C(═O)— linking group, as these phrases are definedhereinabove, with R′ as defined herein.

The term “thiocarbonyl” as used herein, describes a —C(═S)—R′ end groupor a —C(═S)— linking group, as these phrases are defined hereinabove,with R′ as defined herein.

The term “oxo” as used herein, describes a (═O) group, wherein an oxygenatom is linked by a double bond to the atom (e.g., carbon atom) at theindicated position.

The term “thiooxo” as used herein, describes a (═S) group, wherein asulfur atom is linked by a double bond to the atom (e.g., carbon atom)at the indicated position.

The term “oxime” describes a ═N—OH end group or a ═N—O— linking group,as these phrases are defined hereinabove.

The term “hydroxyl” describes a —OH group.

The term “alkoxy” describes both an —O-alkyl and an —O-cycloalkyl group,as defined herein.

The term “aryloxy” describes both an —O-aryl and an —O-heteroaryl group,as defined herein.

The term “thiohydroxy” describes a —SH group.

The term “thioalkoxy” describes both a —S-alkyl group, and a—S-cycloalkyl group, as defined herein.

The term “thioaryloxy” describes both a —S-aryl and a —S-heteroarylgroup, as defined herein.

The “hydroxyalkyl” is also referred to herein as “alcohol”, anddescribes an alkyl, as defined herein, substituted by a hydroxy group.

The term “cyano” describes a —C≡N group.

The term “isocyanate” describes an —N═C═O group.

The term “isothiocyanate” describes an —N═C═S group.

The term “nitro” describes an —NO₂ group.

The term “acyl halide” describes a —(C═O)R″″ group wherein R″″ ishalide, as defined hereinabove.

The term “azo” or “diazo” describes an —N═NR′ end group or an —N═N—linking group, as these phrases are defined hereinabove, with R′ asdefined hereinabove.

The term “peroxo” describes an —O—OR′ end group or an —O—O— linkinggroup, as these phrases are defined hereinabove, with R′ as definedhereinabove.

The term “carboxylate” as used herein encompasses C-carboxylate and O—carboxylate.

The term “C-carboxylate” describes a —C(═O)—OR′ end group or a —C(═O)—O—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “O-carboxylate” describes a —OC(═O)R′ end group or a —OC(═O)—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

A carboxylate can be linear or cyclic. When cyclic, R′ and the carbonatom are linked together to form a ring, in C-carboxylate, and thisgroup is also referred to as lactone. Alternatively, R′ and O are linkedtogether to form a ring in O-carboxylate. Cyclic carboxylates canfunction as a linking group, for example, when an atom in the formedring is linked to another group.

The term “thiocarboxylate” as used herein encompasses C-thiocarboxylateand O-thiocarboxylate.

The term “C-thiocarboxylate” describes a —C(═S)—OR′ end group or a—C(═S)—O— linking group, as these phrases are defined hereinabove, whereR′ is as defined herein.

The term “O-thiocarboxylate” describes a —OC(═S)R′ end group or a—OC(═S)— linking group, as these phrases are defined hereinabove, whereR′ is as defined herein.

A thiocarboxylate can be linear or cyclic. When cyclic, R′ and thecarbon atom are linked together to form a ring, in C-thiocarboxylate,and this group is also referred to as thiolactone. Alternatively, R′ andO are linked together to form a ring in O-thiocarboxylate. Cyclicthiocarboxylates can function as a linking group, for example, when anatom in the formed ring is linked to another group.

The term “carbamate” as used herein encompasses N-carbamate andO-carbamate.

The term “N-carbamate” describes an R″OC(═O)—NR′— end group or a—OC(═O)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “O-carbamate” describes an —OC(═O)—NR′R″ end group or an—OC(═O)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

A carbamate can be linear or cyclic. When cyclic, R′ and the carbon atomare linked together to form a ring, in O-carbamate. Alternatively, R′and O are linked together to form a ring in N-carbamate. Cycliccarbamates can function as a linking group, for example, when an atom inthe formed ring is linked to another group.

The term “carbamate” as used herein encompasses N-carbamate andO-carbamate.

The term “thiocarbamate” as used herein encompasses N-thiocarbamate andO-thiocarbamate.

The term “O-thiocarbamate” describes a —OC(═S)—NR′R″ end group or a—OC(═S)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-thiocarbamate” describes an R″OC(═S)NR′— end group or a—OC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

Thiocarbamates can be linear or cyclic, as described herein forcarbamates.

The term “dithiocarbamate” as used herein encompasses S-dithiocarbamateand N-dithiocarbamate.

The term “S-dithiocarbamate” describes a —SC(═S)—NR′R″ end group or a—SC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-dithiocarbamate” describes an R″SC(═S)NR′— end group or a—SC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “urea”, which is also referred to herein as “ureido”, describesa —NR′C(═O)—NR″R′″ end group or a —NR′C(═O)—NR″— linking group, as thesephrases are defined hereinabove, where R′ and R″ are as defined hereinand R′″ is as defined herein for R′ and R″.

The term “thiourea”, which is also referred to herein as “thioureido”,describes a —NR′—C(═S)—NR″R′″ end group or a —NR′—C(═S)—NR″— linkinggroup, with R′, R″ and R′″ as defined herein.

The term “amide” as used herein encompasses C-amide and N-amide.

The term “C-amide” describes a —C(═O)—NR′R″ end group or a —C(═O)—NR′—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “N-amide” describes a R′C(═O)—NR″— end group or a R′C(═O)—N—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

An amide can be linear or cyclic. When cyclic, R′ and the carbon atomare linked together to form a ring, in C-amide, and this group is alsoreferred to as lactam. Cyclic amides can function as a linking group,for example, when an atom in the formed ring is linked to another group.

The term “guanyl” describes a R′R″NC(═N)— end group or a —R′NC(═N)—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “guanidine” describes a —R′NC(═N)—NR″R′″ end group or a—R′NC(═N)—NR″— linking group, as these phrases are defined hereinabove,where R′, R″ and R′″ are as defined herein.

The term “hydrazine” describes a —NR′—NR″R′″ end group or a —NR′—NR″—linking group, as these phrases are defined hereinabove, with R′, R″,and R′″ as defined herein.

As used herein, the term “hydrazide” describes a —C(═O)—NR′—NR″R′″ endgroup or a —C(═O)—NR′—NR″— linking group, as these phrases are definedhereinabove, where R′, R″ and R′″ are as defined herein.

As used herein, the term “thiohydrazide” describes a —C(═S)—NR′—NR″R′″end group or a —C(═S)—NR′—NR″— linking group, as these phrases aredefined hereinabove, where R′, R″ and R′″ are as defined herein.

As used herein, the term “alkylene glycol” describes a—O—[(CR′R″)_(z)—O]_(y)—R′″ end group or a —O—[(CR′R″)_(z)—O]_(y)—linking group, with R′, R″ and R′″ being as defined herein, and with zbeing an integer of from 1 to 10, preferably, from 2 to 6, morepreferably 2 or 3, and y being an integer of 1 or more. Preferably R′and R″ are both hydrogen. When z is 2 and y is 1, this group is ethyleneglycol. When z is 3 and y is 1, this group is propylene glycol. When yis 2-4, the alkylene glycol is referred to herein as oligo(alkyleneglycol).

When y is greater than 4, the alkylene glycol is referred to herein aspoly(alkylene glycol). In some embodiments of the present invention, apoly(alkylene glycol) group or moiety can have from 10 to 200 repeatingalkylene glycol units, such that z is 10 to 200, preferably 10-100, morepreferably 10-50.

The term “silanol” describes a —Si(OH)R′R″ group, or —Si(OH)₂R′ group or—Si(OH)₃ group, with R′ and R″ as described herein.

The term “silyl” describes a —SiR′R″R′″ group, with R′, R″ and R′″ asdescribed herein.

As used herein, the term “urethane” or “urethane moiety” or “urethanegroup” describes a Rx-O—C(═O)—NR′R″ end group or a —Rx-O—C(═O)—NR′—linking group, with R′ and R″ being as defined herein, and Rx being analkyl, cycloalkyl, aryl, alkylene glycol or any combination thereof.Preferably R′ and R″ are both hydrogen.

The term “polyurethane” or “oligourethane” describes a moiety thatcomprises at least one urethane group as described herein in therepeating backbone units thereof, or at least one urethane bond,—O—C(═O)—NR′—, in the repeating backbone units thereof.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in a nonlimiting fashion.

Experimental Methods

Shore A Hardness was determined in accordance with ASTM D2240

Elastic Modulus (Modulus of Elasticity) was determined from theStrength-Strain curves, in accordance with ASTM D412

Tensile Strength was determined in accordance with ASTM D412.

Z tensile strength was determined in accordance with ASTM D412 uponprinting in the Z direction.

Elongation was determined in accordance with ASTM D412.

Z Elongation was determined in accordance with ASTM D412 upon printingin the Z direction.

Tear Resistance (TR) was determined in accordance with ASTM D 624.

O-ring Tear test was performed as depicted in FIGS. 1A-C, and measuresthe time until a tested objected is broken.

More specifically, an object featuring two O-rings connected by a tube,as depicted in FIG. 1A, and having the following dimensions: necklength: 50 mm; X length: 110 mm; Y length: 30 mm; Z length: 10 mm, isstretched using a stretching device depicted in FIG. 1B, as depicted inFIG. 1C. The time at which the model remains stretched until it isbroken is measured, and represents “static” Tear Resistance, namely,resistance to static tension in an elongated state (lower thanelongation at break).

Before measurements are performed, the printed object (typically matt,printed in HS (high speed) mode is washed with water, using a jettingstation, and is subjected to Conditioning and drying for 24 hours at labconditions.

3D inkjet printing was performed using Triplex/C500 3D inkjet printingsystem, operated at HS mode, unless otherwise indicated.

Mold preparations were obtained according to ASTM 412. Briefly, siliconemolds featuring dimensions according to ASTM 412 were used. The testedformulation was poured into the mold, and a silicon film was used tocover the mold. The formulation was cured for 3 hours in a UV chamber atroom temperature, and samples were thereafter removed gently from themold. 24 hours later, samples were measured according to ASTM D412.

Formulations were prepared by mixing all components at room temperatureunless otherwise indicated. Powder components such as photo initiatorswere dissolved at 85 degrees for 30 minutes.

“Mill base” formulations were prepared by grinding/dispersing the silicain high concentration in one of the curable monomers (for example, at aconcentration of about 20% or about 25%, by weight), to thereby obtain a“mill base” and thereafter adding mill base to the formulation so as toachieve a final concentration as indicated.

Results

Table 1 below presents the components of a reference formulation,referred to herein also as Reference A, currently used to provide a softrubbery material characterized by Shore A hardness of about 27, by 3DInkjet printing, the components of a soft rubbery material according toexemplary embodiments of the present invention, referred to herein asElastomer A, and the mechanical properties of objects printed onTriplex/C500 3D inkjet printing system, operated at HS mode, using therespective formulation.

TABLE 1 Reference A Elastomer A (Wt. %) (Wt. %) silica R7200  0  4Curable mono-functional 15-25 15-25 monomer Elastomeric mono- 55-6555-65 functional curable material Elastomeric multi- 10-20 10-20functional curable material Inhibitor 0-2 0-2 Photo-initiator 1-5 1-5Surfactant   0-0.1   0-0.1 dispersant 0-1 0-1 Tensile Strength (MPa)  1-1.1 2.4-3   Elongation (%) 170-220 260-320 O-ring tear test 15-25minutes 3-6 days Hardness (Shore) 27 30 Tear Resistance (N/m) 3500 5000-8000

Table 2 below presents the components of another reference formulation,referred to herein also as Reference B, currently used to provide aharder rubbery material characterized by Shore A hardness of about 60,by 3D Inkjet printing, the components of a harder rubbery materialaccording to exemplary embodiments of the present invention, referred toherein as Elastomer B, and the mechanical properties of objects printedon Triplex/C500 3D inkjet printing system, operated at HS mode, usingthe respective formulation.

TABLE 2 Reference B Elastomer B (Wt. %) (Wt. %) silica R7200 0 8Elastomeric mono- 30-50 30-50 functional curable material Elastomericmulti-functional 30-50 10-30 curable material Curable mono-functional20-30 20-30 monomer Inhibitor 0-1 0-1 Photo-initiator 1-5 1-5 Dispersant0-2 0-2 special black paste 0-1 0-1 Surfactant 0-1 0-1 Tensile (MPa) 2.2± 0.2  4.04 ± 0.11 Elongation (%) 69 ± 6  146 ± 4 Hardness (Shore) 6045-50 Tear Resistance (N/m) 4000 10200 ± 640

Additional formulations, containing similar components, and varioustypes of silica, at various concentrations, were prepared and tested.

All formulations included the reactive and non-reactive components(except from the silica R7200) as described herein for Elastomer A,Table 1, and the following silica nanoparticles were used:

Silica R7200, which is also referred to in the art as AEROSIL® R 7200,is a methacrylate-functionalized fumed silica. Silica R7200 is anexemplary hydrophobic reactive silica according to the presentembodiments.

Colloidal Silica and Silica nanopowder are exemplary hydrophilic silica.The colloidal silica used herein was obtained as silica particlesdispersed in a mono-functional curable material

Silica nanopowder (10-20 nm particle size) was obtained from Sigma (CatNo. 637238).

Silica R8200, which is also referred to in the art as AEROSIL® R8200, isan exemplary hydrophobic silica according to the present embodiments.

Table 3 below presents the data obtained for objects prepared in a moldfrom a tested formulation and for printed objects prepared from therespective formulation as described hereinabove.

TABLE 3 Tensile % silica Strength Elongation Object silica Silica type(wt.) (MPa) (%) Mold None (Reference — 0 1.25 331 A) Mold Aerosil ® 90hydrophilic 3 1.45 357 Mold Aerosil ® R8200 hydrophobic 5 1.40 323 MoldColloidal silica hydrophilic 4 1.75 325 Mold Colloidal silicahydrophilic 10 2.2 220 Mold Aerosil ® R7200 Hydrophobic 5 1.95 265 andreactive Printed Nanopowder Hydrophilic 10 3.6 250 (Sigma 10 nm silica)Printed Aerosil R7200 Hydrophobic 4 2.4-3 260-320 and reactive

Table 4 below presents comparative mechanical properties of a printedobject made of the formulation denoted as Reference A (see, Table 1),and the same formulation to which 4% or 10% (by weight) of colloidalsilica was added.

TABLE 4 4% 10% Reference A colloidal silica colloidal silica Tensilestrength (MPa) 1.05 1.75 2.2 Elongation (%) 236 325 220 Z Tensilestrength 0.45 1 1 (MPa) Z Tensile elongation 165 300 160 (%) O-ring tear(days) 25 minutes 5-6 5-6 Shore hardness 25 28 37

FIG. 7 presents the effect of various concentrations of hydrophobic,acrylic coated fumed silica, silica R7200, when added to a rubberymaterial formulation presented as Reference A, on the stress-straincurves of a 3D inkjet-printed object made of the respective formulation.

FIG. 8 presents the effect of various concentrations of hydrophobic,acrylic coated fumed silica, silica R7200, and of 10% (hydrophilic)colloidal silica, when added to a rubbery material formulation presentedas Reference A, and denoted as “T”, on the stress-strain curves of a 3Dinkjet-printed object made of the respective formulation.

FIG. 9 presents a water pipe connector printed using an exemplaryformulation according to some embodiments of the present invention (lefttube) and a water pipe connector printed using a formulation which doesnot contain silica (right tube), upon being fitted on a water tube for10 hours. As shown, the elastomeric part with no silica was torn after10 hours, and the part containing silica remained intact, and holds forweeks (data not shown).

The data presented herein demonstrate that using sub-micron silica, suchas (acrylic-functionalized) fumed silica or colloidal silica, in anamount of up to 15% weight percent of a UV curable formulation used toproduce an elastomer by 3D printing, improves the mechanical propertiesof the printed part.

A particularly significant improvement is shown in the Tear Resistanceof the printed rubbery object.

Printed acrylic elastomers are typically very sensitive to tear. Forexample, in POLYJET™ printing, printed fine parts made of acrylicelastomers are often torn during support removal by water jet. Partsthat when utilized are subjected to constant elongation are also oftentorn after a time period of from a few minutes to a few hours.

When fine silica particles are added to the formulation, the TearResistance under constant elongation is increased from minutes to days,without compromising elongation. See, for example, Tables 1-4 3.

In addition to improvement of the Tear Resistance of a printed object,the addition of silica particles does not affect or even increaseselongation of the printed object; results in improvement of the Elasticmodulus, for example, by 2-folds, and even 3-folds; and/or results inreduced surface tackiness of the printed object, without substantiallycompromising other mechanical properties.

Both hydrophobic and hydrophilic silica have similar effects, with moresubstantial improvement demonstrated for hydrophobic silica andparticularly with acrylic-functionalized silica, probably as a result ofinteractions with acrylic monomers in the formulation.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

What is claimed is:
 1. A formulation system comprising a curableelastomeric material and silica particles, the formulation systemcomprising one or more formulations, wherein a weight ratio of a totalweight of said elastomeric curable material and a total weight of saidsilica particles in the formulation system ranges from 30:1 to 4:1,wherein an amount of said elastomeric curable material in theformulation system is at least 40%, or at least 50%, by weight, andwherein said elastomeric material is an acrylic elastomer; and theformulation system further comprises at least one elastomericmono-functional curable material; at least one elastomericmulti-functional curable material and at least one additionalmono-functional curable material.
 2. The formulation system of claim 1,wherein at least a portion of said silica particles comprisefunctionalized silica particles.
 3. The formulation system of claim 2,wherein at least a portion of said silica particles are functionalizedby curable functional groups.
 4. The formulation system of claim 1,wherein an amount of said silica particles in the formulation systemranges from 1 to 20, or from 1 to 15, or from 1 to 10, percent byweight.
 5. The formulation system of claim 1, further comprising atleast one additional curable material.
 6. The formulation system ofclaim 1, further comprising at least one additional, non-curablematerial.
 7. The formulation system of claim 1, wherein a totalconcentration of said curable mono-functional material ranges from 10%to 30%, by weight.
 8. The formulation system of claim 1, wherein a totalconcentration of said elastomeric mono-functional curable materialranges from 50% to 70%, by weight.
 9. The formulation system of claim 1,wherein a total concentration of said elastomeric multi-functionalcurable material ranges from 10% to 20%, by weight.
 10. A kit comprisingthe formulation system of claim 1.